^ Single is an official release. It usually has an A and B side. It's not just a promoted song on radio. If you wanna do a single, you mean the whole thing, release, package and songs.
For instance, LOVE&GIRLS is a single. Its A side would be "Love & Girls", while its B would be "Lingua Franca". Using this example, if you tag your review "[SINGLE] Love & Girls", you would be reviewing the entire single: both songs, the packaging, the release.
On the other hand, if you used the [SONG] tag, we would assume you're just reviewing the one song.