Chavrusa
Chavruta or chavrusa (חַבְרוּתָא, from Aramaic for fellowship) is a traditional Rabbinic approach to learning in which pairs study a shared text in discussion and debate. It is a primary learning method used yeshivot, where participants will often acquire regular study partners of similar ability. The traditional phrase is to learn "in chavrusa", that is, in partnership: the word has come by metonymy to refer to the study partner as an individual, though it would more logically describe the pair.
This tradition may originate in the fact that many Tannaim and Amoraim regularly dispute with a particular other Rabbi in the Talmud in matters of Jewish law. A simple explanation would be that the two were regular study partners. It is alluded to in the saying in Pirke Avot: "Find yourself a teacher, and get yourself a friend (chaver)".