Pls explain the difference

Simply this:

AirPrint is printing to a printer wirelessly

Airplay is playing a video from your iPad to a external monitor via AppleTV or Apple adapter cables.

Actually, Airplay implies a wireless playing ability. So, using wifi, Airplay will allow you to stream music, video, or photos to any device that supports Airplay. It is better than bluetooth in that it uses your wifi and thus doesn't have the same range limitations. As long as the send and receive device is on wireless, then the link can be accomplished. And that is without fidelity loss for music. Video is more complex because it can take a lot more bandwidth to stream video. But the AppleTV is the device most will have that supports Airplay. Others could be speakers and receivers, or Airport Express.