Definition - What does Sati mean?
Sati is a Buddhist term derived from the Pali sati and its Sanskrit counterpart, smrti. It can be translated to mean "mindfulness" or "awareness."
Sati is a spiritual or psychological faculty that forms an essential part of Buddhist practice. It is the first of the seven elements of enlightenment, and the seventh element of the Noble Eightfold Path. Most traditional schools of Buddhism view sati as one of the key elements of meditation.
Western yoga practitioners usually understand sati as the awareness/attention that encourages them to be in the present moment while they improve their focus on bodily postures and the breath.
Yogapedia explains Sati
There are four foundations of sati: mindfulness of body, mindfulness of feelings, mindfulness of mind or dharma, and mindfulness of mental objects.
Sati is often discussed and focused on in a yoga practice. It requires awareness, memory and attention. The practice of mindfulness (specifically, "right mindfulness") pushes the individual to keep the mind alert and aware of the phenomena that affect the body and mind. It’s about being deliberate and attentive, making sure the mind is protected from greed, distraction and distress.
For sati, or mindfulness, to become “right mindfulness,” it requires an understanding of the ethics and wisdom of the practice, along with an exercise of the meditative aspects of the Eightfold Path. The eight limbs, divided into three main divisions (ethics, meditation and wisdom) are the yoga taught by Buddha. The foundations of sati are often taught in the context of meditation.