An acoustic guitar is a modern form of guitar descended from the Classical guitar, but generally strung with steel strings for a brighter, louder sound. Much heavier construction is required to withstand the added tension. Sometimes the term steel-stringed guitar or folk guitar is used to differentiate from the classical guitar.
The acoustic guitar is often played with one or more guitar picks, small plates of hard plastic or other material used to strike and strum the strings. Most players use a flat pick held between the thumb and index finger. A few use fingerpicks, picks worn on the thumb and three fingers. Fingerstyle acoustic guitar players use fingerpicks or use their bare fingers and fingernails to strum and strike individual notes.
One variation on the standard acoustic guitar is the 12 string guitar, which sports an additional doubling string for each of the traditional six strings. This guitar was made famous by artists such as Huddie Leadbetter (a.k.a. Leadbelly), Pete Seeger, and Leo Kottke.