kriyā-tantra (Sanskrit). ‘Action tantra’, a term used for the first of the four late classificatory categories of tantra in Buddhism. This group of tantras largely represent the earliest developmental phase of tantric Buddhism and comprises key works such as the Susiddhikāra Tantra, the Subāhu-paripṛcchā, the Sarva-maṇḍala-sāmānya-vidhi-guhya Tantra and the Dhyānottara-paṭala. According to later Indo-Tibetan exegesis, this class of tantras primarily teach external, object-based practices and rituals.

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