The Masoretic Text (MT) is the Hebrew text of the Jewish Bible (Tanakh). It defines not just the books of the Jewish canon, but also the precise letter-text of the biblical books in Judaism, as well as their vocalization and accentuation for both public reading and private study. The MT is also widely used as the basis for translations of the Old Testament in Protestant Bibles, and in recent decades also for Catholic Bibles.
The MT was primarily copied, edited and distributed by a group of Jews known as the Masoretes between the seventh and tenth centuries CE. Though the consonants differ little from the text generally accepted in the early second century (and also differ little from some Qumran texts that are even older), it has numerous differences of both greater and lesser significance when compared to (extant 4th century) manuscripts of the Septuagint, a Greek translation (made in the 3rd to 2nd centuries BCE) of the Hebrew Scriptures that was in popular use in Egypt and Palestine and that is often quoted in the Christian New Testament.
The Hebrew word mesorah (מסורה, alt. מסורת) refers to the transmission of a tradition. In a very broad sense it can refer to the entire chain of Jewish tradition (see Oral law), but in reference to the masoretic text the word mesorah has a very specific meaning: the diacritic markings of the text of the Hebrew Bible and concise marginal notes in manuscripts (and later printings) of the Hebrew Bible which note textual details, usually about the precise spelling of words.
The Talmud (and also Karaite mss.) states that a standard copy of the Hebrew Bible was kept in the court of the Temple in Jerusalem for the benefit of copyists; there were paid correctors of Biblical books among the officers of the Temple (Talmud, tractate Ketubot 106a). This copy is mentioned in the Aristeas Letter (§ 30; comp. Blau, Studien zum Althebr. Buchwesen, p. 100); in the statements of Philo (preamble to his "Analysis of the Political Constitution of the Jews") and in Josephus (Contra Ap. i. 8).