Vāsanā (Sanskrit; Devanagari: वासना) is a behavioural tendency or karmic imprint which influences the present behaviour of a person. It is a technical term in Indian religions, particularly Buddhist philosophy and Advaita Vedanta.
Vāsanā (Devanagari: वासना, Tibetan: བག་ཆགས, Wylie: bag chags) and its near homonym vasana (Devanagari: वसन) are from the same Indo-European linguistic root, sharing a common theme of 'dwelling' or 'abiding'.
Keown (2004) defines the term generally within Buddhism as follows:
"vāsanā (Skt.). Habitual tendencies or dispositions, a term, often used synonymously with bīja (‘seed’). It is found in Pāli and early Sanskrit sources but comes to prominence with the Yogācāra, for whom it denotes the latent energy resulting from actions which are thought to become ‘imprinted’ in the subject's storehouse-consciousness (ālaya-vijñāna). The accumulation of these habitual tendencies is believed to predispose one to particular patterns of behaviour in the future."
Sandvik (2007: unpaginated) states that:
... bag chags, in Sanskrit vāsanā. This word is used a lot in presentations about karma. It means habitual tendencies, subtle inclinations that are imprinted in the mind, like a stain. For example, if someone smokes, there will be a habitual tendency for an urge to smoke every day, usually around the same time. There are bigger picture bag chags, such as why some people are kind by nature, and others are cruel; it's the tendency to behave in a certain way that will trigger similar actions in future, reinforcing the bag chags.
Lusthaus states that the Cheng Weishi Lun (Chinese: 成唯識論), a commentary on Vasubandhu's Triṃśikā-vijñaptimātratā, lists three types of vāsanā, which are synonymous with 'bija' or 'seeds':