Static Friction The friction experienced by a body, when it is at rest is known as static friction.
Dynamic Friction The friction experienced by a body, when it is in motion is called dynamic friction. It is also called as kinetic friction.

A vibration in which the element moves to and fro in a direction perpendicular to the direction of the advance of the wave is called transverse vibration.

When the motion between a pair is limited to a definite direction irrespective of the direction of force applied, then the motion is said to be a completely constrained motion.