What is "abhyasa"

Abhyāsa, in Hinduism, is a spiritual practice which is regularly and constantly practised over a long period of time. It has been prescribed by the great sage Patanjali Maharishi in his Yoga Sutras, and by Lord Krishna in the Bhagavad Gita as an essential means to control the mind, together with Vairāgya.

Sutra 1:12 "Both practice (abhyāsa) and non-reaction ( vairāgya) are required to still the patterning of consciousness."

Sutra 1:13 "Practice is the sustained effort to rest in that stillness."—as translated by Chip Hartranft in his work The Yoga Sutra of Patanjali.