1) A musical instrument that is not
electric
2) A musical performance that uses no electric instruments (
aside from
microphones and similar amplification)
1) Jimi Hendrix played an electric guitar on the song "Purple Haze", but
Paul Simon played an acoustic guitar on Simon &
Garfunkel's "Mrs. Robinson". Techno and dance music uses electric drums, but rock music typically sticks to acoustic drums.
2)
Eric Clapton's band did an acoustic show on "Mtv Unplugged".