Waves exhibit phenomena like reflection, refraction, diffraction, and interference.
Light and sound do all that, so we consider them (prior to the 20th century anyway) to be waves. They have wavelengths and frequencies like waves.
Light is an electromagnetic phenomenon. Sound is a pressure wave that travels through a medium (like air).
We see when light comes through our eyeball and excites special cells on our retina that evolved to sense light. We hear when sound comes in our ear and mechanically vibrates our eardrum. Our inner ear has mechanisms to sense the vibration of the eardrum and transmit the information to the brain.
