Headless CMS
Also known as: API first CMS, decoupled CMS
A content system that stores the words and hands them to anything that asks, without deciding how the page looks.
A traditional content system stores the content and draws the page. A headless one only does the first half. It keeps the content and serves it to whatever you built the front of the site with.
The appeal is reuse. The same content can feed a website, an app and a screen in a shop window without being typed three times.
For most small shop client work this is more machinery than the job needs. You now run two systems instead of one, and a client who wants a headline changed is depending on both of them being healthy.
Reach for it when a client genuinely publishes to several places. Not because it sounds modern.