An mp3 is a type of encoding for audio and music files on a computer.
Usually an mp3 file is encoded or "ripped" from Compact Disc track, or a less compressed (larger) audio file like a WAV or an AIFF.
These mp3 files have special information stored inside them called id3 tags. The id3 tags describe the artist, album, and track number of a song. The accuracy and amount of information included in the mp3 file depends on what information is available to the encoding software at the time the mp3 file is encoded or ripped.
For Ubuntu users, you can easily view this information from the command line by installing the following programs:
sudo apt-get install id3
sudo apt-get install id3v2
Ta-da! Now you can do stuff like this:
$id3v2 --list "Midnight Voyage.mp3"
TPE1 (Lead performer(s)/Soloist(s)): Ghostland Observatory
TIT2 (Title/songname/content description): Midnight Voyage
TALB (Album/Movie/Show title): Paparazzi Lightning
TRCK (Track number/Position in set): 10
TYER (Year): 2006
TCON (Content type): Electronic (52)