Euler

Gimbal lock
Gimbal lock is a loss of one degree of freedom (DOF) in a 3D rotation system due to the alignment of two rotational axes.
For example when PITCH is ±90° the YAW and ROLL axes rotate around the YAW and we loss on degree of freedom
Euler Angles Gimbal Visualization

colors
roll (x) - blue pitch (y) - green yaw (z) - green
rotate pitch 90 degree make roll and yaw rotation to the same direction
Rotation Order
Euler (XYZ)
RPY