CSS stands for cascading style sheets. Its used as a way of defining display elements on an html web page (eg fonts, and their sizes... whether there is a border around pictures etc). If you do web design, you *need* to know CSS. Its easy to learn and implement.
Cascading Style Sheets
If ever you want to know about any aspect of web design... go to w3.org... thats the organisation which determines how web pages will work and its then up to browser makers to make sure their browser can read the html.
Of course, you may have meant to ask about CSC which is something different and I will leave someone else to define it
