Wikipedia
Form criticism is a method of biblical criticism that classifies units of scripture by literary pattern and then attempts to trace each type to its period of oral transmission. Form criticism seeks to determine a unit's original form and the historical context of the literary tradition.
Form criticism was originally developed for Old Testament studies by Hermann Gunkel. Martin Noth, Gerhard von Rad, and other scholars, who used it to supplement the documentary hypothesis with reference to its oral foundations. It later came to be applied to the Gospels by Karl Ludwig Schmidt, Martin Dibelius, Rudolf Bultmann, and Robert M. Price among others.
Over the past few decades, form criticism's emphasis on oral tradition has waned in Old Testament studies. This is largely because scholars are increasingly skeptical about our ability to distinguish the "original" oral traditions from the literary sources that preserve them. As a result, the method as applied to the Old Testament now focuses on the Bible's literary genres, becoming virtually synonymous with genre criticism.