A Linear Hyperdrive is an advanced hyperdrive technology created by Earthfleet, and deployed on the Raven, Wolfpack and Mythos class starships, as well as the rebuilt Generation 3 Sergenious. It that gets its unique name from the method in which it operates and ultimately produces FTL flight. Namely, the drive's power curve increases linearly, and is only limited in top speed by how much energy you can push through the system, or how much plasma pressure that the nacelles can withstand. The top end speed of a linear hyperdrive has not yet been discovered, even though it has already been proven to be able to cross vast distances in a matter of days or hours that would take a comparable warp drive powered vessel months or even years to cover the same distance. The Linear Hyperdrive is, more or less, a 3rd generation hyperdrive, with Coaxial Drive being the unofficial second generation of the technology.
This is because hyperdrive research and advancement more or less stopped not long after the creation of the first hyperdrives, and didn't resume again until picked up by the scientists of the Brayburn Society as a means to replace warp technology, which they felt was unsafe and insufficient for their needs. After refining and perfecting hyperdrive technology through the Coaxial Drive, they took it a step further in the creation of Linear Hyperdrive, leading to an FTL system that was superior in every way to every other FTL technology ever used, either past or present. The only technology that is faster, although nowhere near as safe, is Jump Drive, which is something the Razkor unfortunately discovered.