Buddha-kula (Sanskrit, Buddha family). A term especially associated with tantric Buddhism and used to categorize and allocate the various Buddhas, Bodhisattvas, other deities and also initiates into groups. Early tantric texts utilize a threefold system, the three Buddha families, comprising the Tathāgata Family associated with Śākyamuni or Vairocana, the Vajra Family associated with Vajrapāṇi or Akṣobhya, and the Lotus Family associated with Avalokiteśvara or Amitābha. Later tantric traditions employ a fivefold system, the five Buddha families or Five Jinas, correlated to the five awarenesses (pañca-jñāna) or aspects of enlightenment (bodhi), comprising the Tathāgata family (Vairocana), the Vajra family (Akṣobhya), the Jewel family (Ratnasaṃbhava), the Lotus family (Amitābha) and the Action family (Amoghasiddhi).

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