A spike drive is a method of faster-than-light (ftl) travel. This drive was invented in 2108 by Dr. Tiberius Crohn, and allowed humanity to travel across the stars for the first time. It was mostly replaced by the jump gate network in the core sectors of human space, but continued to be used in areas of the frontier that hadn't been connected to the network.
The drive 'drills' into a dimension called 'drillspace', or 'metaspace' and the ship then travels through this dimension to its destination where it subsequently drills out and enters 'real space' again. This drillspace can be quite dangerous as anyone who finds themselves outside the ship will be violently returned to real space - ending up in pieces across a large area of space.
To correctly use a spike drive, navigators have to correctly calculate a drill course. Failing to do this can result in the ship being thrown wildly off course and the drive system destroyed, possibly stranding the ship at a location from which it can't return.
Spike drives are subdivided into six categories, rated 1-6, with a rating 1 drive being the lowest and slowest class of drives.