1: A guitar that uses a large resonance box to amplify and broadcast sound. Generally mellower than other kinds of guitars. Since it doesn't require an amp to be heard, it's much more portable than an electric. Often combined with mics or pre-amps for playing in venues.
2: A type of guitar often used at parties by music-illiterate dicks trying to steal your girlfriend.
1: "I really love the tone on this Takamine acoustic guitar. The cedar construction really gave it a warm sound."
2: Guy with acoustic guitar: *singing* I gave my love a cherry / That had no stone / I gave my love a chicken / That had no bones / I gave my love a story / That had no end / I gave my...
Bluto: *grabs the guitar and smashes it against the wall* Sorry. - Animal House