Sādhanā, literally "a means of accomplishing something", is an ego-transcending spiritual practice. It includes a variety of disciplines in Hindu, Buddhist, Jain and Sikh traditions that are followed in order to achieve various spiritual or ritual objectives.
In particular, sādhanā can refer to a tantric liturgy or liturgical manual, that is, the instructions to carry out a ritual.
The historian N. Bhattacharyya provides a working definition of the benefits of sādhanā as follows:
Religious sādhanā, which both prevents an excess of worldliness and molds the mind and disposition (bhāva) into a form which develops the knowledge of dispassion and non-attachment. Sādhanā is a means whereby bondage becomes liberation.
Iyengar (1993: p. 22) in his English translation of and commentary to the Yoga Sutras of Patanjali defines sādhanā in relation to abhyāsa and kriyā:
Sādhanā is a discipline undertaken in the pursuit of a goal. Abhyāsa is repeated practice performed with observation and reflection. Kriyā, or action, also implies perfect execution with study and investigation. Therefore, sādhanā, abhyāsa, and kriyā all mean one and the same thing. A sādhaka, or practitioner, is one who skillfully applies...mind and intelligence in practice towards a spiritual goal.
Example via www.ramdass.org: Making it Sacred
Example via www.mindpodnetwork.com: The Teacher by Chogyam Trungpa