Kriyatantra

The Outer Tantras are the second three divisions in the ninefold division of practice according to the Nyingma school of Tibetan Buddhism. This system divides the whole of the Buddhist path into three divisions of three and is in contrast to the division of the Sarma, or New Translation schools (Gelug, Kagyu and Sakya) which use a fourfold division. The three divisions of the Outer Tantra correspond to the lower three category of tantras of the New Translation (Sarma) schools.

The three divisions of the Outer Tantras are:

As well as being differentiated in terms of emphasis in practice, the three categories of Outer Tantra are also textual categories, with lists of texts assigned to each category; for which see the individual articles for each section.

The stages of the lower tantras can be divided into 4 parts; empowerments; vows and commitments; close retreats; common and uncommon attainments. Every tantra requires the empowerment of a guru in order to enter and proceed along the path, and normally there are a number of different empowerments for different practices, and in addition the Bodhisattva and Tantric vows must be taken. A close retreat involves intense sessions of meditation in the practice of deity yoga (concentration on one's personal yidam and their mantra), and the common and uncommon attainments are the occult powers, or siddhis, that are obtained as a result of that practice.

The Mañjusrimulakalpa, which later came to classified under Kriyatantra, states that mantras taught in the Saiva, Garuda and Vaisnava tantras will be effective if applied by Buddhists since they were all taught originally by Manjushri.

Charyatantra (performance tantra), is the second of the outer tantras, and although it maintains a strong emphasis on external ritual actions, like Kriyatantra, the emphasis is now upon obtaining liberation through meditation. It is therefore externally similar to kriya tantra, and internally similar to Yogatantra. The empowerments required are similar to that of kriyatantra, except there is a 4-fold vase empowerment.

...
Wikipedia