Rel

A rel was a Dalek unit of measurement, principally of time.

The Daleks used rels for time measurement. (DW: Doomsday) One rel was slightly longer than a second. (DW: Evolution of the Daleks)

In other contexts, it was a unit of speed, where presumably rel is short for some standard unit of distance per rel. (DC: Plague of Death) A rel was also used as a unit to measure hydroelectric energy, not to be confused for a vep, the unit used for artificial sunlight (DWA: The Dalek Book)

Behind the Scenes
The word Rel first appeared in the non-canonical movie Dr. Who and the Daleks and in comics, but had never appeared in the TV series until the 2006 episode Doomsday, during which Dalek Sec told the other Daleks of the Cult of Skaro to rewind a recording back nine rels.