Ösel (n):  (pronounced 'od gsal') 

Sanskrit: Prabashvara

Clarity, Luminosity, Radiant Light, referring to the intrinsic purity of the substratum of the mindstream.

Ösel is the basic “knowing” quality of the mind in which nothing is excluded.  In this context, luminosity simply refers to the cognitive capacity or awareness, which is the defining characteristic of a mind.