A Coaxial Drive is an advanced form of Hyperdrive capable of traveling through the subspacial layers of space/time, facilitating faster than light (FTL) travel in the process. The system is powered by a coaxial generator, from which the drive gets its name, and creates FTL flight by injecting plasma into sets of nacelles which, in turn, create the necessary energy fields required to initiate FTL flight. The generator itself creates this plasma, which is also used to power the ship, by drawing energy from inter-dimensional space through a complex series of steps. The original particle that was used to create this energy is then recycled through the generator to create still more energy, thus in turn creating a perpetual or "coaxial" loop. This is how the generator gets its name. Ships equipped with Coaxial Drives tend to be 40% faster than their warp powered counterparts. However, the advantages that this boost in speed provide are offset by a rather nasty and sometimes fatal flaw that can result in the generator either stalling, resulting in the ship losing all power, or suffering a fatal runaway condition that results in an explosion and loss of the ship. The Coaxial Drive, while an exceptional and revolutionary technology for its time, is only used by Earthfleet for several decades before it is eventually abandoned in favor of the newer, safer and more powerful Linear Hyperdrive, and its companion Quantum Power Core, both of which eliminate the issues suffered by the Coaxial Drive and are surprisingly resilient in comparison.
Also, as a point of note, the coaxial drive used in the Earthfleet universe is NOT the same as the one mentioned in Star Trek. That's because the latter is more closely related to Jump Drive technology, whereas the Coaxial Drive, used by Earthfleet, is a Nacelle based Hyperdrive technology powered by a Coaxial power core. So, while the two technologies share the same name, they are entirely different FTL technologies employing entirely different means of FTL flight.