A unit is a single, indivisible entity that forms part of something larger. It can refer to a physical object or concept that has specific characteristics and properties, and can be used as a measure, standard, or category for classification. In mathematics, science, and engineering, a unit is a fundamental element or building block from which larger structures are formed, and it often represents a quantity of one type (such as length, mass, or time). The term "unit" can also refer to a group or individual that forms part of an organization, military force, or other collective.