Euler angles
An orientation described as three successive rotations about three axes — often yaw, pitch and roll.
Named after Leonhard Euler in the 18th century. Three numbers, read in a fixed order (say X-Y-Z), are enough to pin down any orientation, and they are easy for a human to read: yaw, pitch and roll match how we already think about an aircraft's attitude.
The price is three traps. Order matters, so the same three numbers mean different things under different conventions; they can't be interpolated cleanly between two orientations; and they suffer from gimbal lock. That is why game engines often expose Euler angles in the editor but store the rotation internally as a quaternion.