Megillah is the tenth Tractate

Talmud

The Talmud is a central text of mainstream Judaism. It takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs and history....

 of Mishnah

Mishnah

The Mishnah or Mishna is the first major written redaction of the Jewish oral traditions called the "Oral Torah". It is also the first major work of Rabbinic Judaism. It was redacted c...

 in the Order Moed

Moed

Moed is the second Order of the Mishnah, the first written recording of the Oral Torah of the Jewish people . Of the six orders of the Mishna, Moed is the third shortest. The order of Moed consists of 12 tractates:# Shabbat: or Shabbath deals with the 39 prohibitions of "work" on the Shabbat...

. It and its Gemara

Gemara

The Gemara is the component of the Talmud comprising rabbinical analysis of and commentary on the Mishnah. After the Mishnah was published by Rabbi Judah the Prince The Gemara (also transliterated Gemora or, less commonly, Gemorra; from Aramaic גמרא gamar; literally, "[to] study" or "learning by...

 deal with the laws of Purim

Purim

Purim is a Jewish holiday that commemorates the deliverance of the Jewish people in the ancient Persian Empire from destruction in the wake of a plot by Haman, a story recorded in the Biblical Book of Esther .Purim is celebrated annually according to the Hebrew calendar on the 14th...

 and offers exegetical understandings to the Book of Esther

Book of Esther

The Book of Esther is a book in the Ketuvim , the third section of the Jewish Tanakh and is part of the Christian Old Testament. The Book of Esther or the Megillah is the basis for the Jewish celebration of Purim...

. It also includes laws

Halakha

Halakha — also transliterated Halocho , or Halacha — is the collective body of Jewish law, including biblical law and later talmudic and rabbinic law, as well as customs and traditions.Judaism classically draws no distinction in its laws between religious and ostensibly non-religious life; Jewish...

 concerning the public reading of the Torah

Torah reading

Torah reading is a Jewish religious ritual that involves the public reading of a set of passages from a Torah scroll. The term often refers to the entire ceremony of removing the Torah scroll from the ark, chanting the appropriate excerpt with special cantillation, and returning the scroll to...

 and other communal synagogue

Synagogue

A synagogue is a Jewish house of prayer. This use of the Greek term synagogue originates in the Septuagint where it sometimes translates the Hebrew word for assembly, kahal...

practices. There is also a segment in the first chapter which details certain miscellaneous laws.
(A megillah is a finely detailed account or book but the term by itself commonly refers to the Book of Esther.)