How does the title relate to the book, The Wave?
Scientifically, a wave is a surge of energy that moves across the surface of a liquid. This surge of energy is not localized by nature, but is diffuse and cannot be isolated at one point. By nature, a wave is in motion and spreads across a surface.
The story of this book functions similarly. The notion introduced by Mr. Ross quickly spreads across the student body of the class, eliminating individuality. The idea of the wave is diffuse and collective in its nature. This is a large part of its appeal. This also means that no one person can be said to represent the Wave. It is a movement and a philosophy as much as it is a group of people.
This is especially true during the early stages of the Wave.