Best answer by IXK
Usually a tag is a label that informs about the style of the track ( or playlist) . You can also choose other key words, that you feel represent the feel of the music ( e.g. 'deep' , 'epic' , 'love', 'sexy'...) , or put the name of the album, name of the artist, the track's name even etc.
Hope that helps. Let me know in case you need more help.