Thruster is a UI setting for a group or an object. It propels an object along the objects Y axis in a fashion similar to a rocket or jet engine. This function can be used to create aircraft and increase traction on a vehicle etc
There are many known uses for the thruster, even in it's infancy. The current uses range from propulsion of sea vehicles to firing a missile sky high.
How to change the Axis
By default, the axis of the thruster is the Y axis.
If you want to change it, rotate the group axis.