Tags

Tagging is adding pieces of information describing the song. They are stored in the header of the audio file. This makes the file self documenting.
Windows Audio has its on tagging schema.
MP3's are tagged with IDV3
Tagging in WAV is not supported. Something to keep in mind if you want to transfer WAV-files to another computer. In case of WAV you better don't rely on tagging but on a file structure with descriptive file names.

More about tagging can be found here