Understanding .swc files

Hi,

I have been using Flash, Actionscript 3.0 (learning) and TweenLite but never heard about .swc files until today when I was reading a tutorial and the author mentioned about downloading the greensock.swc file which I have never heard before.

Can someone explain what a .swc file is, what it does? Because it looks like you can convert your .as files into a .swc files.

I Google it but I didn’t find a good definition (at least I didn’t understand it).

Thanks