Houses of Hillel and Shammai
The House of Hillel (Beit Hillel) and House of Shammai (Beit Shammai) were two schools of thought in Jewish scholarship during the period of the Zugot (transl. pairs). The houses were named after the sages, Rabbi Hillel and Rabbi Shammai (of the last century BCE and the early 1st century CE), who founded them. These two schools had vigorous debates on matters of ritual practice, ethics, and theology, which were critical for shaping the Oral Torah and, later, Rabbinic Judaism as it is today.
The Mishnah mentions the disagreement of Hillel and Shammai as one that had lasting positive value for Jewry and Judaism:
Every dispute that is for the sake of Heaven, will in the end endure; But one that is not for the sake of Heaven, will not endure. Which is the controversy that is for the sake of Heaven? Such was the controversy of Hillel and Shammai. And which is the controversy that is not for the sake of Heaven? Such was the controversy of Korah and all his congregation.
In most cases (though not always), Hillel's opinion was the more lenient and tolerant of the two. In nearly all cases, Hillel's opinion was accepted as normative by Halakha and remains in effect.