Gravitic propulsion is thrust generated without pushing against anything else, such as that generated by a space drive. There are three types of gravitic propulsion.
(As mentioned above) Drives that use some sort of field effect (i.e. electric/magnetic/gravitational) to generate thrust. Such as; disjunction drives, induction ring drives, diametric drives, or bias drives.
Drives attempting to utilize the behavior of gyroscopic motion to generate unidirectional motion.
Drives that attempt to use the inertia of mechanical movements of un-balanced masses to generate unidirectional motion.
Electro-gravitic propulsion exists, for the most part, only in the realm of science fiction. NASA scientists toy with the ideas, but the theoretical physics behind them are just so far out there. On the other hand, gyro and Inertio-gravitic drives are simple enough to be built in the workshops of any skilled craftsman. Weather or not they actually work is something else altogether.
Contrary to it's name, gravitic propulsion doesn't necessarily have anything to do with gravity (don't blame me, I didn't invent the term).