Inertial Navigation Systems (INS) are devices used to determine the position and orientation of a moving object without relying on external references. They utilize a combination of accelerometers and gyroscopes to measure changes in velocity and rotation, allowing the system to calculate its current location based on initial position data. INS are commonly used in various applications, including aircraft, submarines, and missiles. They provide accurate navigation information even in environments where GPS signals are unavailable, making them essential for military and aerospace operations.