What is the X in X-mas?
the title accorded to the Jewish spiritual leaders and scholars who headed Talmudic academies that flourished, with lengthy interruptions, from the 7th to the 13th century in Babylonia and Palestine. The chief concern of the geonim was to interpret and develop Talmudic Law and to safeguard Jewish legal traditions by adjudicating points of legal controversy. Their replies (responsa) were quoted far beyond the limits of their own communities and are of great value in studying the Jewish history and theology of the period. The geonim continued a tradition of scholarship begun long before by the soferim (teachers and interpreters of biblical law) and kept alive in subsequent centuries by the tannaim and amoraim (who, respectively, produced the compilation of law called the Mishna and wrote commentaries on the Mishna, called Gemara).