The type of mechanical wave whose direction of vibration is perpendicular to its direction of travel is a transverse wave.

Here's a breakdown:

* Mechanical Wave: A wave that requires a medium (like air, water, or a solid) to travel.

* Transverse Wave: A wave where the particles of the medium oscillate perpendicular to the direction the wave travels.

Examples of Transverse Waves:

* Light waves: Although light doesn't require a medium, it behaves as a transverse wave.

* Waves on a string: Think of a guitar string vibrating.

* Water waves: The movement of water particles is up and down, while the wave itself travels horizontally.