The whole point of using a physics engine is to create a world where you put objects (bodies) that behave according to physics laws. The term body is highly based on physics literature, where all the objects that interact are called bodies.
There are three types of bodies in Box2D: static, kinematic, and dynamic. They are explained as follows:
Static bodies: You can think of these as bodies that are fixed to the world. They don't move on their own, and they are not affected by gravity or collisions. Keep in mind that static bodies are able to collide with other objects, but they will not move or change as a result of the collision, just as the other objects (if they're not static). We'll use static bodies as platforms in our game, for our player to stand on.
Kinematic bodies: These bodies are not affected by collisions or gravity either, but they can move on their own. They can affect other objects during collisions, as statics bodies do. A simple moving platform hazard...