A CSS framework, also known as web design framework is an already prepared library of styles that is meant to allow for easier, more standards-compliant styling of a web page. Just like programming and scripting language libraries, CSS frameworks package a number of ready-made options for designing and outlaying a web page. This definition of CSS framework is found on Wikipedia but I think CSS framework is simply an easier way to get things done in web design.
In this article I am not going to list all or well known CSS frameworks instead I will only list the CSS frameworks that I actually used.