i looked up the word "song" out of curiosity. apparently it does only refer to a piece of music that has vocals. 1. a short metrical composition intended or adapted for singing, esp. one in rhymed stanzas; a lyric; a ballad. 2. a musical piece adapted for singing or simulating a piece to be sung: Mendelssohn's Songs without Words. but the word is commonly used to mean music with or without vocals.