MP3 is an audio compression codec that allows users to compress songs, speeches, and monkey sounds (Yes, they're out there...) dramatically without noticeable loss of quality. MP3 stands for Motion Picture Experts Group Audio Layer 3 (MPEG Audio Layer 3), and because its ability to compress songs, it became de facto standard for music distribution over the web. Actually, it's quite simple (in concept, that is). What MP3 codec does, is that it gets rid of parts of audio that you and I cannot hear. Our human ears are quite limited in that after hearing something loud, you can't hear quiet sound for short period of time. MP3 codec calculates and deletes that part. This is how MP3 achieves its great compression ratio without the apparent quality loss.