This site currently has a song-lyrics tag with about ten questions. However, it seems to me that the "song" part of "song lyrics" is redundant; the word lyrics implies that the question is about a song.
I was going to say "make it so", but then thought about it a bit more ...
We don't lose anything by having a slightly longer tag name. You might argue that it's redundant, but while small redundancies can be irritating to us pedants, they don't really harm the site. It's not as if the tag name is approaching the 25-character limit.
The longer name may help for clarity. I could easily imagine people who think all poetry counts as "lyrics", but they might be less likely to associate the phrase "song lyrics" with poetry. If the longer name helps to make the tag's intended purpose clearer, then it's worth keeping.
People might search for the tag using "song" rather than "lyrics". As Mithrandir mentions, it would be nice to have this tag pop up as a suggestion when people type
songinto the tag box.
(The middle one of these three points is most important.)