noun: The loss of one degree of freedom in the three-dimensional rotational movement of a three-gimbal mechanism, which occurs when the axes of two of the three gimbals are driven into a parallel configuration, so that the system's rotational movement becomes two-dimensional (and necessarily remains so until an appropriate force is applied); the equivalent situation in a simulation of rotational movement, when the mathematical model uses Euler angles (representing pitch, yaw and roll) or their equivalent.
