Thruster is a UI setting for a group or an object. It propels an object along the objects Z(blue) 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 its infancy. The current uses range from propulsion of sea vehicles to firing a missile sky high. It is possible to make the thruster try to point at a certain object by putting into the text box "lookAt("[insert object name here]")
How to change the Axis
By default, the axis of the thruster is the Z(blue) axis.
If you want to change it, rotate the group to the wanted axis.