Of the several types of Vedic sacrifices, the Jyotiṣṭoma is also one, belonging to the Soma group. Its standard form is the Agniṣṭoma.
Stoma (= praise) is a form of chanting the stotras (Ṛgvedic chants) in which the verses are increased by repetition to a certain number. So, a stoma is known by a number. For example: trivṛt-stoma (three fold or nine).
In the Jyotiṣṭoma sacrifice, the four stomas that are chanted are: trivṛt, pañcadaśa, saptadaśa and ekaviṁśa. These are called four jyotis or lights. Hence the name Jyotiṣṭoma.
See also AGNIṢṬOMA.