A content management system, or CMS, is the software layer that lets someone create, edit, and publish website content through an editor interface instead of writing HTML directly. Under the hood it usually separates content from presentation, so a single template change can update the look of hundreds of pages without touching their text.
WordPress, Joomla, and Drupal are among the most widely used, with WordPress alone running a large share of the web. For SEO, the CMS a site runs on shapes what's easy and what's a fight: how cleanly it handles URL structure, whether it lets you set title tags and meta descriptions per page, how it generates (or fails to generate) a sitemap, and how much page speed gets eaten by plugins and themes stacked on top of the core system. Headless and static-site setups have grown as an alternative, decoupling content management from the rendering layer, trading some editorial convenience for tighter control over performance and markup.
