It is a song recording of more or less 10 minutes. The single has often two sides : A & B.
On A-Side, we usually have one or two songs we find on the album of an artist or group. Most of the time, the song is released to promote the album. We can find a « radio edit » and/or the « album version » of the song.
On B-Side, we can find for instance, an acoustic version, an instrumental, a remix or a bonus track.