Sadhana (from the SANSKRIT root sadh, complete, accomplish) is used generically for any spiritual practice but is most frequently used to refer to Hindu TANTRIC practice.
Further reading: Pandit Madhav Pundalik, Bases of Tantra Sadhana (Pondicherry: Dipti, 1972); Sir John Woodroffe and Swami Pratyagatmananda, Sadhana for Self-Realization: Mantras, Yantras and Tantras (Madras: Ganesh, 1963).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.