The Gemara and the Mishnah together form the Talmud. The Mishnah is the base text, and the Gemara is the commentary and analysis that completes it. The term “Gemara” comes from the Hebrew word גמר (gamar), which means “to complete” or “to study” in Aramaic. The rabbis of the Mishnah are known as Tannaim, and the rabbis of the Gemara are called Amoraim. Due to the existence of two groups of commentaries, there are actually two versions of the Talmud: the Talmud Yerushalmi (Jerusalem Talmud) and the Talmud Babli (Babylonian Talmud), corresponding to the Gemara of the Land of Israel and Babylon, respectively. Both versions share the same Mishnah. The Gemara is mostly written in Aramaic, with the Jerusalem Gemara in Western Aramaic and the Babylonian Gemara in Eastern Aramaic. However, both versions contain passages in Hebrew, sometimes even switching languages within a single story. In contrast, the language of the entire Mishnah is Hebrew.
Source: Shiva Shambho
Books on Gemara