Feeling happy? Feeling sad? Sing a song! A song is poetry set to music, and there’s a song for every occasion, from “Happy Birthday” to “Here Comes the Bride.” Tra la la!
Most songs have words, or lyrics, though not all of them do — and we call the musical sound a bird makes a song as well. Sometimes rhyming poems are called songs, like Pablo Neruda's "April Rain Song." If your friend tells you she bought her bicycle "for a song," that simply means it was inexpensive, not that she actually had to sing a song to get it.