---
title: "Glossary"
description: "The Éclair glossary defines 50 terms from CMS, SEO, GEO, security, hosting and AI, each with the lesson that covers it in more depth."
url: "https://eclair.academy/en/docs/glossary"
lang: "en"
author: "Thierry Gustin"
published: "2026-11-02"
updated: "2026-11-02"
---

# Glossary

> **Key takeaways** — This Éclair glossary defines 50 terms you come across while building your site, from API key to WebP: static cache, slug, meta description, JSON-LD, GEO, llms.txt, MCP, OAuth 2.1, two-factor authentication, CSP, Lighthouse, .htaccess, DNS… Each definition takes one or two sentences and links to the lesson that covers the topic in depth.

This Éclair glossary gathers the technical words you come across in the admin, in the lessons and in the official documentation. Each term has a short, accurate definition, followed by a link to the lesson that goes further. The 50 terms are sorted alphabetically; an acronym is filed under its first letter.

## How do you use this Éclair glossary?

- Search for a word with your browser's search (`Ctrl+F`, or `Cmd+F` on a Mac).
- The exact labels from the admin are written in bold, like **Settings › SEO**.
- For words that belong to a specific screen (a field, a block, a file), also see the [Reference for the 18 blocks](https://eclair.academy/en/docs/blocks), the [Settings reference](https://eclair.academy/en/docs/settings) and [Files, folders and URLs](https://eclair.academy/en/docs/files).

## A to C

- **API key**: a secret identifier that lets your site use a pay-as-you-go service, such as Claude or ChatGPT. Éclair encrypts it on your server and never shows it in full. See [Turning on the built-in AI assistant](https://eclair.academy/en/paths/ai-mcp/ai-assistant).
- **Argon2id**: a password hashing algorithm, described in [RFC 9106](https://datatracker.ietf.org/doc/html/rfc9106). Éclair uses it with 19 MiB of memory and 2 passes, and falls back on bcrypt if the server doesn't support it. See [Everyday security](https://eclair.academy/en/paths/intermediate/everyday-security).
- **Art direction**: a complete visual world (5 colors, a heading font, layouts) that goes further than a theme. Éclair offers 12 of them, all adjustable, and the AI can imagine 3 based on your business. See [Art directions and Design score](https://eclair.academy/en/paths/intermediate/art-directions).
- **Block**: a unit of content in the editor, such as a paragraph, an image, a FAQ or a banner. Éclair offers 18, which you insert by typing `/` on an empty line. See the [Reference for the 18 blocks](https://eclair.academy/en/docs/blocks).
- **Canonical URL**: a tag that tells search engines the official URL of a page when several URLs show the same content. Éclair adds one to every page; the editor's SEO tab lets you point to a different one. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **CLS (Cumulative Layout Shift)**: a measure of how much the layout shifts while the page loads, assessed by Lighthouse. Explicit image dimensions and the preloaded heading font prevent these shifts. See [Performance: keeping 100 out of 100](https://eclair.academy/en/paths/expert/performance).
- **CMS (content management system)**: software that manages a site's content from an admin, without writing code. Éclair is a PHP CMS with no database. See [Discover Éclair CMS](https://eclair.academy/en/paths/beginner/discover-eclair).
- **CSP (Content Security Policy)**: an HTTP header that tells the browser which scripts, styles and images it may load ([MDN guide](https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/CSP)). Éclair's policy allows no inline scripts. See [Éclair's architecture](https://eclair.academy/en/paths/expert/architecture).
- **CSRF (cross-site request forgery)**: an attack that tricks your browser, while you're logged in to the admin, into sending an action without your knowledge. Éclair puts a token on every action and checks where requests come from. See [Everyday security](https://eclair.academy/en/paths/intermediate/everyday-security).

## D to G

- **Design score**: the third score in the Analysis tab, alongside SEO and GEO. It checks the heading hierarchy, the banner, the buttons, the features and the quality of the text. See [Art directions and Design score](https://eclair.academy/en/paths/intermediate/art-directions).
- **DNS (Domain Name System)**: the directory that links a domain name to the address of the server hosting the site. A change can take a while to propagate. See [Preparing your installation](https://eclair.academy/en/paths/beginner/prepare-installation).
- **E-E-A-T**: experience, expertise, authoritativeness and trustworthiness, the criteria Google describes for judging the quality of content ([Google Search Central](https://developers.google.com/search/docs/fundamentals/creating-helpful-content)). In Éclair, the author's bio, their profiles and the visible dates all contribute. See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).
- **Flat files**: storing data in plain files rather than in a database. Éclair keeps each piece of data in a protected `.php` file in the `data/` folder. See [Files, folders and URLs](https://eclair.academy/en/docs/files).
- **Focus keyphrase**: the word or group of words a page targets in search engines. The SEO analysis checks that it appears in the title, the meta description, the URL, the introduction and a subheading. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **FTP and SFTP**: protocols for uploading files to your hosting; SFTP encrypts the connection. A program such as [FileZilla](https://filezilla-project.org/) handles both. See [Install Éclair step by step](https://eclair.academy/en/paths/beginner/install-eclair).
- **GEO (generative engine optimization)**: optimizing a site so that it's understood and cited by answer engines such as ChatGPT, Perplexity, Gemini or Claude. Éclair calculates a GEO score for each piece of content. See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).

## H to L

- **H1, H2, H3**: the heading levels of a web page. The H1 is the page title, and there's only one; the H2 to H4 subheadings structure the content without skipping a level. See [Write and publish your first post](https://eclair.academy/en/paths/beginner/first-article).
- **hreflang**: an attribute that tells search engines about a page's versions in other languages. Éclair adds it, along with an `x-default` version, when you link translations. See [Creating a multilingual site](https://eclair.academy/en/paths/intermediate/multilingual-site).
- **HSTS (HTTP Strict Transport Security)**: a header that forces the browser to use only HTTPS for a site. Éclair offers it as an option, for one year, in **Settings › Advanced**. See [Advanced security and maintenance](https://eclair.academy/en/paths/expert/advanced-security).
- **.htaccess**: a configuration file read by Apache and LiteSpeed. Éclair's version rewrites URLs, protects the internal folders, compresses pages and sets browser caching. See [Files, folders and URLs](https://eclair.academy/en/docs/files).
- **IndexNow**: a protocol that notifies Bing, Yandex, Seznam and other search engines every time you publish ([indexnow.org](https://www.indexnow.org/)). You turn it on in **Settings › SEO**. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **JSON-LD**: a structured data format, using the schema.org vocabulary, inserted into the page to describe it to search engines: organization, article, breadcrumbs, FAQ, product… See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **Key takeaways**: a 2- or 3-sentence summary (25 to 90 words) shown at the top of a post, which AI engines readily quote. See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).
- **LCP (Largest Contentful Paint)**: the time it takes to display the largest visible element on the page, measured by Lighthouse. Éclair gives loading priority to the main image. See [Performance: keeping 100 out of 100](https://eclair.academy/en/paths/expert/performance).
- **Let's Encrypt**: a free certificate authority that provides the HTTPS certificates of almost every host ([letsencrypt.org](https://letsencrypt.org/)). See [Preparing your installation](https://eclair.academy/en/paths/beginner/prepare-installation).
- **Lighthouse**: Google's audit tool, built into Chrome, which scores a page's performance, accessibility, best practices and SEO out of 100. See [Performance: keeping 100 out of 100](https://eclair.academy/en/paths/expert/performance).
- **LiteSpeed**: a web server compatible with Apache's `.htaccess` files, common at shared hosts. Éclair runs on it with no special configuration. See [Choosing your hosting](https://eclair.academy/en/hosting).
- **llms.txt**: a text file in Markdown format, proposed by [llmstxt.org](https://llmstxt.org/), that presents a site to AI. Éclair generates `/llms.txt` and `/llms-full.txt`; Google says it doesn't use them for its search engine ([note of June 15, 2026](https://developers.google.com/search/updates)). See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).

## M to O

- **Markdown**: a plain-text syntax (headings with `#`, lists with `-`) that AI reads easily. Éclair publishes a `.md` version of every page. See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).
- **MCP (Model Context Protocol)**: an open standard, launched by Anthropic in November 2024, that connects AI to tools ([modelcontextprotocol.io](https://modelcontextprotocol.io/)). Éclair's connector lets Claude or ChatGPT read your site and prepare drafts. See [Understanding the MCP connector](https://eclair.academy/en/paths/ai-mcp/understanding-mcp).
- **Merchant Center**: a Google service where merchants list their products to appear for free in the Shopping tab. Éclair provides the `/products.xml` feed to add there. See [Selling with the lightweight shop](https://eclair.academy/en/paths/intermediate/shop).
- **Meta description**: the text shown under a page's title in search results. Éclair's analysis aims for 110 to 160 characters. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **Nginx**: a web server that ignores `.htaccess` files, so Éclair's rules have to be reproduced in its configuration. See [Nginx, VPS, proxy and CDN](https://eclair.academy/en/paths/expert/nginx-vps).
- **noindex**: an instruction asking search engines not to index a page. In the editor, it's the **Don’t index this page (noindex)** checkbox. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **OAuth 2.1**: an authorization framework that lets an app act on a service without knowing your password ([oauth.net](https://oauth.net/2.1/)). Éclair's MCP connector uses it, after your explicit approval. See [Understanding the MCP connector](https://eclair.academy/en/paths/ai-mcp/understanding-mcp).
- **Open Graph**: tags that define the title, description and image of a page shared on social media. Éclair generates the 1200 × 630 share image. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).

## P to S

- **Payment link**: a payment page hosted by Stripe, PayPal or Revolut Business for a fixed-price product. The **Buy now** button on an Éclair product page leads there. See [Selling with the lightweight shop](https://eclair.academy/en/paths/intermediate/shop).
- **PHP-FPM**: a process manager that runs PHP for a web server such as Nginx ([PHP manual](https://www.php.net/manual/en/install.fpm.php)). See [Nginx, VPS, proxy and CDN](https://eclair.academy/en/paths/expert/nginx-vps).
- **PKCE (Proof Key for Code Exchange)**: an OAuth safeguard, described in [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636), that prevents an authorization code from being hijacked. Éclair requires it for the MCP connector. See [Understanding the MCP connector](https://eclair.academy/en/paths/ai-mcp/understanding-mcp).
- **Redirect (301)**: a permanent redirect from an old URL to a new one, without losing search rankings. Éclair creates one when you change the URL of published content. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **robots.txt**: a file that tells bots what they may crawl. Éclair writes your policy for 30 AI bots and the sitemap URL into it. See [GEO: getting cited by AI](https://eclair.academy/en/paths/intermediate/geo-ai-search).
- **Shared hosting**: a server shared by many sites, the cheapest kind of hosting. Éclair is designed to run on it. See [Choosing your hosting](https://eclair.academy/en/hosting).
- **Sitemap**: an XML file that lists a site's URLs for search engines. Éclair's sitemap, at `/sitemap.xml`, includes images and language versions. See [SEO with Éclair](https://eclair.academy/en/paths/intermediate/seo).
- **Slug**: the part of the URL that belongs to a piece of content, like `my-post` in `/blog/my-post`. Keep it short, lowercase and with the focus keyphrase. See [Write and publish your first post](https://eclair.academy/en/paths/beginner/first-article).
- **Static cache**: an HTML copy of each page, saved in `cache/pages/` and then served by `index.php` without loading the application. Éclair clears it on every change. See [Éclair's architecture](https://eclair.academy/en/paths/expert/architecture).

## T to W

- **Theme**: a 1.5 to 3 KB stylesheet that changes colors and typography without changing the HTML. Éclair ships with 6. See [Themes and appearance](https://eclair.academy/en/paths/intermediate/themes-appearance).
- **Topic cluster**: a group of pages on the same topic, organized around a pillar page and connected by internal links. In Éclair, each category serves as a pillar page, and the editor suggests your pages when you create a link. See [Blog, categories and topic clusters](https://eclair.academy/en/paths/intermediate/blog-categories).
- **Two-factor authentication (2FA, TOTP)**: a second login factor, a 6-digit code that changes every 30 seconds in an app (TOTP standard, [RFC 6238](https://datatracker.ietf.org/doc/html/rfc6238)). Éclair also provides 8 backup codes. See [Everyday security](https://eclair.academy/en/paths/intermediate/everyday-security).
- **WCAG (Web Content Accessibility Guidelines)**: the W3C's accessibility guidelines ([overview](https://www.w3.org/WAI/standards-guidelines/wcag/)). Éclair adjusts colors to meet their contrast thresholds: 7:1 for an art direction's text, 4.5:1 for links and buttons. See [Art directions and Design score](https://eclair.academy/en/paths/intermediate/art-directions).
- **WebP**: a lightweight image format designed by Google. Éclair creates WebP versions of your images at 480, 800, 1200 and 1600 px. See [Images and the media library](https://eclair.academy/en/paths/beginner/images-media-library).

> **Missing a word?** — This Éclair glossary grows with each release. If a term stops you, look for it first in the [frequently asked questions](https://eclair.academy/en/faq), then report it from the [Contact](https://eclair.academy/en/contact) page.

## Frequently asked questions about the glossary

### What's the difference between SEO and GEO?

SEO targets traditional search engines (Google, Bing), while GEO targets answer engines, which write an answer and cite their sources (ChatGPT, Perplexity, Gemini, Claude). Éclair calculates both scores in the editor's Analysis tab.

### What's the difference between a theme and an art direction?

A theme changes colors and typography with a 1.5 to 3 KB stylesheet. An art direction changes the whole visual world: palette, heading font, corners, spacing, and the layout of the banner and features.

### Are the terms in the Éclair glossary specific to Éclair?

Most are standard web terms, which the Éclair glossary defines as the CMS uses them. A few belong to the software itself, such as “Key takeaways”, the Design score or the art direction.