The term "x-1" can refer to various concepts depending on the context. In mathematics, it often represents a simple expression where "x" is a variable, and "1" is a constant. The expression "x - 1" indicates the value of "x" decreased by one, which is a fundamental operation in algebra. In technology, "X-1" may refer to specific models or versions of products, such as the X-1 Rocket Plane, which was an experimental aircraft that first broke the sound barrier. This plane played a significant role in the development of supersonic flight and advanced aeronautical research.