Define the terms wave and wave motion. Explain the formation of waves with the help of an example.

Wave: The repeated vibrations of the particles of the medium, creates a disturbance which travels through a medium is called a wave. The disturbance moves from one particle to the next particle.

Wave motion: The motion of the disturbance is called wave motion.

Let us look at the wave formation using an example. 
When we drop a pebble into a pond of still water, a circular pattern of alternate crests and troughs spreads out from the point where the pebble strikes the water surface. The particle oscillates as a result of kinetic energy of the pebble. The oscillating particles, in turn, transfer energy to the particles of next layer which also begin to oscillate. Energy is further transferred to the next layer of particle. This way energy is transferred from one particle to another particle.