Short answer
A content management system (CMS) is software for creating, organizing and publishing content without editing application code for every change. It usually provides an editor, media management and user permissions. WordPress is one example; a CMS is a category, not a particular technology.
The problem a CMS solves
A restaurant manager should be able to change opening hours without commissioning a software release. A publisher should be able to draft an article, send it for review and schedule it. The CMS gives those tasks an interface and a workflow.
WordPress combines content management with themes and an extension system. Other approaches separate the content backend from the site that displays it, often called a headless CMS.
A CMS is not necessarily a page builder
A page builder focuses on visual composition. A CMS manages the underlying content and publishing workflow. One product may provide both, but they answer different questions: “How does this page look?” and “Who can change this information, and where is it used?”
Nor is a CMS the same as a host. Your content software still needs somewhere to run, even if a vendor bundles the services together.
What to ask before choosing one
Start with the people updating the site. What changes each week? Does content need approval? Must the same product details appear on multiple channels? Who owns exports and backups?
Then assess the technical fit and maintenance cost. The WordPress project’s description is a useful concrete example of a publishing system and its ecosystem, not proof that all CMS products work identically.
Vibe coding can produce a custom editing interface. Before replacing a CMS with one, check whether you are also rebuilding permissions, revisions, previews, accessibility and export tools. A text box is not the whole publishing system.