Ānāpānasati is mindfulness of the in-breath and out-breath. The discourse devoted to it describes sixteen steps through body, feelings, mind and mental states, and says that, developed, it fulfils the four foundations of mindfulness, the seven factors of awakening, and knowledge and liberation.
Ānāpānasati
Mindfulness of breathing: a basic Buddhist meditation, the Buddha’s own practice on the night of awakening.
Also: Anapanasati, mindfulness of breathing