Why is an MP 3 file called so?

MP 3 is short for MPEG Audio Layer 3.MPEG is the short form for Moving Picture Experts Group,which  developed a compression system used for audio data.Uncompressed audio files are too large.The MP 3 format is a compression system for audio files like musics,talks,etc

Its reduces the number of bytes in a song without affecting the quality of the song,so the computer takes less space.The aim of MPEG-3 or MP 3 is to compress a song by the factor of 10 to 14 without clearly affecting its sound quality 

Mp 3 or Mp 4 sounds similar,but they are rather different.MPEG-4 is a media container format used to store media of many types on a computer.