five Buddha families 

The fivefold classificatory system for Buddhas, Bodhisattvas, and other divine beings derived from the middle period Mahāyāna sūtra tradition and adopted by the later tantras. Each family is headed by a particular Buddha endowed with specific qualities. The families are the Tathāgata Family (Vairocana), the Vajra Family (Akṣobhya), the Jewel Family (Ratnasaṃbhava), the Lotus Family (Amitābha), and the Action Family (Amoghasiddhi). The five Buddha family system replaced the earlier three Buddha family scheme.

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