What is meaning of css?

HTML & CSS
1

What is meaning of css. It is mostly use in html. but why.

2

Suggest you Google it and read up on it

3

Now a day answer like that is very easy find just by using a search engine like Google as irishman suggested above.

I usually go to sites like wikipedia.org for general answer:
http://en.wikipedia.org/wiki/Cascading_Style_Sheets

For a more detail answer then I look for sites that are focusing on the topic of interest. For example, for CSS and web design, there is a section for that in about.com:
http://webdesign.about.com/od/xhtml/u/htmlcssxml.htm

Members here may suggest other valuable resources as well as answer to your question directly. There is a bunch of members here that are very knowledgeable of topic like this.

4

CSS stands for Cascading Style Sheets. In addition to the links tom8 suggested, you could look at the SitePoint CSS Reference for more information.