Rel

A rel was a Dalek unit of time measurement. A rel was slightly longer than one Earth second. (DW: Evolution of the Daleks) It appears that a countdown is sometimes measured in gaps of 3 rels (DW: The Daleks)

In other contexts, it is a unit of speed (DC: Plague of Death), where presumably rel is short for some standard unit of distance per rel.

It is also used as a unit to measure hydroelectric energy, not to be confused for a vep, the unit used for artificial sunlight (The Dalek Book (1964))

Behind the Scenes
The concept of a 'Rel' first appeared in the movie Dr. Who and the Daleks, but never appeared in the TV series until the 2006 episode Doomsday, in which Dalek Sec told the other Daleks of the Cult of Skaro to rewind a recording back 9 rels.