jñāna (Sanskrit; Pāli, ñāṇa). General term meaning knowledge, particularly in the context of the understanding of doctrines. In terms of Buddhist epistemology, tradition (anuśrava) is not by itself a valid form of knowledge, nor are sense-perception or reason reliable means of knowledge until the distorting influence of unwholesome mental factors such as the three roots of evil (akuśala-mūla) have been eliminated. Once this has been achieved, one who reflects with right attention (yoniśo manasikāra) will perceive with the proper mode of cognitive awareness and see things ‘as they really are’ (yathābhūta). In later Mahāyāna sources jñāna comes to mean ‘non-conceptualizing’ or ‘non-dual’ awareness, and is sometimes used synonymously for enlightenment (bodhi) itself. Based on the Buddhabhūmi Sūtra and Yogācāra doctrines, the basic Buddha awareness of enlightenment is subdivided according to the function into the five awarenesses (pañca-jñāna).

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

jñāna: 'Knowledge', a mode of prajñā, characterized by decisive (niścita) understanding. Some Sarvāstivāda masters require that knowledge repeatedly discerns the cognitive object. There is a standard set of 10: 1.dharma-jñāna, 2.anvaya-jñāna, 3.duḥka-jñāna, 4.samudya-jñāna, 5.nirodha-jñāna, 6.mārga-jñāna, 7.saṃvṛti-jñāna, 8.paracitta-jñāna, 9.kṣaya-jñāna, 10.anutpāda-jñāna.

Sarvastivada Abhidharma, Sanskrit-English Glossary, by Bhikkhu KL Dhammajoti