How is the term 'sugatagarbha Buddha-Nature' to be understood? It refers to clear light luminosity, which constitutes the fundamental ground of being. The essence of this clear light nature of mind is unsoiled by any sort of imperfection. This clear luminous nature itself is the sugatagarbha [and] it pervades all sentient beings; 'pure being' is present in the mind of beings. "Pure being" is clear-light luminosity by nature, and this is precisely what the Buddha-Nature is.

-- Khenpo Tsultrim Rinpoche