What is CodeIgniter?

[eluser]sean_THR[/eluser]
CodeIgniter is a collection of common libraries that you can re-use without having to write them from the ground up every time. It's not a code editor but rather the code itself. It speeds up development by providing you with already working code that you can use in your own applications.

I'd recommend going through some of the tutorials so that you can get a better understanding of it.