A sublight drive was a vital starship component used to drive ships through realspace at speeds less than the speed of light; the most common form of sublight drive was the ion engine, which the TIE fighter used two of to achieve its incredible speeds.
The usual speeds achieved by sublight drive were quite substantial, amounting to a respectable fraction of the speed of light. A freighter-sized vessel propelled by sublight drive could clear the atmosphere of a planet and its gravity well in a matter of minutes.
The most common sublight drive was produced by Hoersch-Kessel Drive, Inc., and found in vessels ranging from the T-16 skyhopper to the Imperial-class Star Destroyer. Durafly also produced sublight drives.