A 12 string acoustic guitar is a type of guitar that has twelve strings, with six pairs of strings that are tuned in octaves. Each string pair is played together, creating a more complex and rich sound compared to a standard 6-string acoustic guitar. The extra strings also provide more harmonic overtones, making it sound more like a harp or a mandolin. 12-string guitars are mostly used in folk, country, and popular music. Popular brands that make 12-string acoustic guitars include Martin, Taylor, and Guild. Playing a 12-string guitar is more challenging than playing a 6-string guitar, as the strings are closer together and the guitar requires more finger strength and dexterity.