Semde

Semde (Tibetan: སེམས་སྡེ, Wylie: sems sde; Sanskrit: cittavarga) translated as "mind division", "mind class" or "mind series" is the name of one of three scriptural and lineage divisions within Atiyoga, Dzogchen or the Great Perfection which is itself the pinnacle of the ninefold division of practice according to the Nyingma school of Tibetan Buddhism.

Semde emphasizes the clarity (gsal-ba) or the innate awareness (rig-pa) aspect of the Natural State.

Penor Rinpoche states that due to the different approaches of various Dzogchen lineages, three sub-schools have developed of which semde is one. The other two divisions or schools are Longde (Space Series) and Menngagde (Oral Instruction Series). The Mind School is attributed to Sri Singha and Vairotsana's lineage

These three divisions were introduced by the Buddhist scholar Manjushrimitra. As Great Perfection texts, the texts of all three divisions are concerned with the basic primordial state, the nature of mind-itself (which is contrasted with normal conscious mind). They are related to the 'Three statements' of Prahevajra.

It is important to note that the three series do not represent different schools of Dzogchen practice as much as different approaches to the same goal, that being the basic, natural, and primordial state. As is common throughout much Buddhist literature, Tibetan Buddhism in particular, gradations in the faculties of practitioners are also ascribed to the three divisions, they being seen as appropriate for practitioners of low, middling, and high faculties, respectively.

...
Wikipedia