In the case of the TR-3B Black Manta, it means a craft that uses highly pressured mercury accelerated by nuclear energy, so that plasma is produced, which, in turn, creates a field of anti-gravity around the craft. It has an electromagnetic coil at the heart of it’s motive power system, the result of which is electromagnetic drive that interacts with the Higgs-Boson field at the quantum level. Heady stuff indeed!

So, an anti-gravity aircraft doesn’t use conventional turbine or rocket engine technology, but instead a propulsion system that creates thrust by generating high-energy plasma. These aircraft are also referred to as ‘flux liners’.

As with many divergent aviation technologies, anti-gravity technology dates back to the latter part and aftermath of World War II, and specifically the covert U.S. project known as Operation Paperclip.

https://www.youtube.com/watch?v=2KHVJiUwoYI