What is Three Body?
Here's a couple of possibilities:

1. The physical three body problem. This problem is a mathematical issue that occurs when you have three gravitational bodies rotating around a center of gravity. Their combined influence leads to incredible computational difficulty when determining a predicted trajectory. The ultimate result of their interactions is a chaotic random system with no hope of having a general solution that is computable in a finite number of steps.

2. The second possibility is the Three Body Problem, a science fiction novel by Cixin Liu. The novel centers around the consequences of the first contact between humanity and an alien species that lives in a three body star system.
Wouldn't the bodies be orbiting a center of gravity, instead of rotating?
Yes, orbiting is the more appropriate term as rotation could refer to the orientation of the objects themselves.