In 3D games, physics means using the laws of real world physics to make objects move and interact in a realistic way. For example, if your game character pushes a rock off a cliff, the rock will fall until it hits the ground. These laws are not hard coded, which means that you can change the values of certain physical parameters to build your own game mechanics. A common example is changing the amount of gravity present.
Depending on how you want your object to interact in your game, you can choose one of the following types of physics for it: