An acoustic guitar is a musical instrument in the guitar family. Its strings vibrate a sound board on a resonant body to project a sound wave through the air. The original, general term for this stringed instrument is guitar, and the retronym 'acoustic guitar' distinguishes it from an electric guitar, which relies on electronic amplification. Typically, a guitar's body is a sound box, of which the top side serves as a sound board that enhances the vibration sounds of the strings. In standard tuning the guitar's six strings are tuned (low to high) E₂ A₂ D₃ G₃ B₃ E₄.

Guitar strings may be plucked individually with a pick or fingertip, or strummed to play chords. Plucking a string causes it to vibrate at a fundamental pitch determined by the string's length, mass, and tension. (Overtones are also present, closely related to harmonics of the fundamental pitch.) The string causes the soundboard and the air enclosed by the sound box to vibrate. As these have their own resonances, they amplify some overtones more strongly than others, affecting the timbre of the resulting sound.