A seraph (Heb. שׂרף, pl. שׂרפים Seraphim, lat. seraph[us], pl. seraphi[m]) is one of a class of celestial beings mentione once in the Hebrew Bible (Tanakh or Old Testament), in Isaiah. Later Jewish imagery perceived them as having human form, and in that way they passed into the ranks of Christian angels. In the Christian angelic hierarchy, seraphim represent the highest known rank of angels.