asubha: Literally, “the impurities.” Subjects of meditation, which focus on the inherent repulsiveness of the body, recommended especially as powerful antidotes to lust. It can either take the form of seeing a so-called beautiful or desirable person as a skin bag that is full of urine, feces, pus, blood, etc. or it can be done as a “Cemetery Meditation” where you actually watch a body decompose over a period of time.
Not usually done by laypersons unless lust is a particular problem.
In the Girimananda Sutta A. X., 50, however, the Perception of impurity asubha-saññā refers to the contemplation of the 32 parts of the Body see: Kāya-gatā-Sati. The contemplation of the Body's impurity is an effective antidote against the hindrance of sense-desire see: Nīvarana and the Mental distortion Vipallāsa, which sees what is truly impure as pure and beautiful. See XLVI, 51; A. V. 36, Dhp. 7, 8; Sn. 193ff. - The Five Mental Hindrances Wheel 26, pp. 5ff.