The term "000-18" typically refers to a specific model of acoustic guitar produced by the brand Martin. This model is known for its smaller body size, which makes it comfortable to play, especially for those with smaller frames or for younger musicians. The "000" designation indicates the body shape, while "18" signifies the series, which is often associated with a solid wood construction and a warm, balanced tone. The Martin 000-18 is favored by many musicians for its versatility, making it suitable for various genres, including folk, blues, and country. Its rich sound and quality craftsmanship contribute to its popularity among both amateur and professional guitarists.