Re: what is Apache License?
Licensing is a broad and complicated issue, and one I tend to try and stay out of beyond the basics (IANAL.)
But in general, it's a free, open source license that doesn't require redistribution of the source code for a covered work, unlike the GPL which does. It also doesn't "infect" any derived works - whereas with something like the GPL, if you include a GPL based library, your code then has to be distributed under the GPL.
Save the whales, feed the hungry, free the mallocs.