Define: What is a wave?

1. move one's hand to and fro in greeting or as a signal.

2. move to and fro with a swaying or undulating motion while remaining fixed to one point.

3. a long body of water curling into an arched form and breaking on the shore.

4. a sudden occurrence of or increase in a specified phenomenon, feeling, or emotion.

5. a slightly curling lock of hair.

6. a tendency to curl in a person's hair.

7. a periodic disturbance of the particles of a substance which may be propagated without net movement of the particles, such as in the passage of undulating motion, heat, or sound.