what is ogg?

i've had soo many people tell me that ogg is better than mp3, how? i know ogg is opensource, but as long as the bit rate's the same does it really matter in terms of quality? or does the differnce matter in size ?

It uses lossy compression algorithms that are superior to that of MPEG layer 3.  At the same bitrate, OGGs sound better than MP3s.