Chazal or Ḥazal (Hebrew: חז"ל) is an acronym for the Hebrew "Ḥakhameinu Zikhronam Liv'rakha" (חכמינו זכרונם לברכה, "Our Sages, may their memory be blessed"), is a general term that refers to all Jewish sages of the Mishna, Tosefta and Talmud eras, essentially from the times of the final 300 years of the Second Temple of Jerusalem until the 6th century CE.
Amoraim ("expounders"): Refers to the sages of the Talmud who were active during the end of the era of the sealing of the Mishnah, and until the times of the sealing of the Talmud (220CE – 500CE). The Amoraim sages were active in two areas, the Land of Israel, and Babylon. In addition to the Babylonian Talmud and the Jerusalem Talmud, their writings were also preserved in midrashs such as Midrash Rabba.
Savoraim ("reasoners"): Refers to the sages of Beth midrash (Torah study places) in Babylon from the end of the era of the Amoraim (5th century) and until the beginning of the era of the Geonim (From the end of the 6th century or the midst of the 7th century).
Until the end of the Savoraim era, the Chazal had the authority to commentate on the Torah according to the Talmudical hermeneutics standards required by the Halakhah le-Moshe mi-Sinai (The non written laws handed to Moses at Sinai), sometimes even expounding a word or phrase outside of its plain and ordinary sense. Nowadays in Orthodoxy, this authority is not delegated to the current generation's sages, and thus the Torah can not be commentated on, in matters concerning the halakha ("tradition"), if it contradicts the Chazal's commentary.
Until the midst of the Tannaim era, when there was a Sanhedrin (a High Court of Jewish law), Chazal had also the authority to decree restrictions and to enact new religious regulations, in any matter they saw fit, concerning issues that were not included in the written Torah, or were not handed in Biblical Mount Sinai. These rabbinical mitzvot ("commandments") include the holidays of Purim and Hanukkah, the laws of muktzah ("set-aside items") on Shabbat, the ritual washing of one's hands (netilat yadayim) before eating bread, the construction of eruvim (liminal gateways), and the institution of the current schedule of daily prayer services – shacharit (morning prayer), mincha (afternoon prayer), and ma'ariv (evening prayer).