In MANU, gravity is one of the default units of every scene that can be found in the Scene panel. Gravity is applied to all dynamic objects in the Scene, except the Main Character. To learn more about the gravity settings for the Main Character, go to Main Character Settings > Gravity and Mass (link). In physics terms, gravity is the natural force that causes things to fall toward the earth. Gravity is a global setting that is applied to a certain level in a game.
In MANU, the value for gravity is generally fine left at its default, which is -9.78 on the Y axis. It determines the force of gravity in the real world. Changing this value would simulate a lower or higher force of gravity that could vary from -100 to 100.