A warp factor is a term indicating velocity in the subspace realm where faster-than-light (FTL) speeds are possible. Starfleet and the Federation has used a scale using cochrane units to measure the distortion potential of a warp drive. An original (OCU) scale was used up until the early 24th century, whereupon a revised scale (MCU) was put into effect when a more complete understanding of the nature of subspace was reached. (ST reference: Starship Spotter)