MP3 term explained

MP3 - MPeg-1 audio layer 3

MP3s have become very popular on the Internet. Mp3 refers to a file that has been compressed using the MPEG compression software. This reduces the size of the file, while maintaining almost all of the quality.

If you put some MP3s on to a CD and play in an audio CD player, then do the same for a normal CD; it can be difficult to see which is actually better in terms of sound quality. This is how good MP3s are.