wave: a repeating pattern that transfers energy
Mechanical waves move through matter by making molecules bump into each other.
Sound waves are an example of mechanical waves. They start with a disturbance (a vibration) and move through a medium (some kind of matter) by compressing molecules together. The molecules only move slightly, then return to where they were. But the waves continues through the next molecules, and the next, and the next.
Other types of waves don’t need matter to travel through. Electromagnetic waves (which include light as well as radio waves, microwaves, and x-rays) can carry energy through empty space.