Chronon

Chronons were particles which make up time in a similar way to how particles would make up matter or anti-matter. (DW: The Time Monster, Time and the Rani)

Theory
At infinitesimal intervals, time actually existed in these discrete particles. TOMTIT transported matter by slipping it between the empty spaces between chronons. (DW: The Time Monster)

Practical applications
The Doctor called the Daleks' temporal prison by the alternative name of a "chronon loop" (DW: Journey's End)

The Time Lords trapped the Mad Mind of Bophemeral in a single chronon following the Millennium War, in effect trapped it in a time loop. (PDA: The Quantum Archangel)

Behind the Scenes
The chronon only got seriously proposed after the airing of The Time Monster, making this one of the few instances of Doctor Who predicting an advance in science or technology.