The angle between particle velocity and wave velocity in a transverse wave is

In a transverse wave,the particles of the medium:

What is called a transverse wave? And what is called a longitudinal wave?

The type of waves that can be propagated through solids is:

Given below are some examples of wave motion. State in each case if the wave motion is transverse,longitudinal or a combination of both:
$(a)$ Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways.
$(b)$ Waves produced in a cylinder containing a liquid by moving its piston back and forth.
$(c)$ Waves produced by a motorboat sailing in water.
$(d)$ Ultrasonic waves in air produced by a vibrating quartz crystal.

The angle between the particle velocity and wave velocity in a transverse wave is [except when the particle passes through the mean position].