Cubit is a unit of measurement that dates back to ancient times, typically defined as the length of a person's forearm from the elbow to the tip of the middle finger. It is often used in historical contexts, particularly in relation to ancient civilizations like the Egyptians and Mesopotamians, who utilized it in construction and land measurement. The length of a cubit can vary, but it is generally considered to be about 18 inches (45.72 cm). There are different types of cubits, such as the royal cubit, which was longer and used for more precise measurements in architecture and engineering.