C.M.S is short for Content Management Systems.
Content management is the next step in separating structure from design.

What began with Cascading Style Sheets and was furthered by XML, is exploding with the CM environment, where billions were spent last year and more billions are expected to be spent in the years ahead.

C.M. Systems come in many shapes: They can be huge or small, simple or very complex.

They range from the very expensive (almost $300,000 for enterprise–wide systems like http://www.vignette.com/ or http://www.interwoven.com/)
and $43,000 per server processor for www.microsoft.com/cmserver to almost free (less than $1,000 for Manila and nothing for http://www.zope.com/

But they are all based on the same idea:

C.M. allows designers to focus on design by building templates.
Subject experts build content in a separate environment.
The server takes the content, inserts it into the correct template and sends it all, neatly wrapped up, to end users.

But that’s just the technology side of CM systems.