Parashah (pa-rah-SHAH) is the weekly Torah reading(s), or the weekly Torah portion read during services. Parashah means "portion." Parashah formally means a section of a biblical book in the Masoretic text of the Tanakh (Hebrew Bible). In common usage today, the word often refers to the weekly Torah portion (a short form of Parashat ha-Shavua). Each weekly Torah portion adopts its name from one of the first unique word or words in the Hebrew text. Dating back to the time of the Babylonian captivity (6th Century BCE), public Torah reading mostly followed an annual cycle beginning and ending on the Jewish holiday of Sim Chat Torah. The Torah is divided into 54 weekly portions to correspond to the lunisolar Hebrew calendar, which contains up to 55 weeks, the exact number varying between leap years and regular year. There was also an ancient triennial cycle of readings practiced in some parts of the world.
Regular public readings of the Torah were introduced by Ezra the Scribe after the Jewish people's return from the Babylonian captivity (c. 537 BCE), as described in the Book of Nehemiah chapter 8. According to a set of procedures they believed, the practice of Torah reading has remained unchanged in two thousand years since the destruction of the Temple in Jerusalem (70CE). Prior to Ezra, the command of Torah reading was based on Biblical commandment of Hakhel (Deuteronomy 31:10-13), by which once every seven years, the entire people was to be gathered, "men, women, ad children," and hear much of Deuteronomy, the final volume of the Pentateuch, read to them.
Traditionally, the command of gathering the people and reading them the Torah was to be performed by the king. Under Ezra, Torah reading became more frequent, and the congregation themselves substituted for the king's role. Ezra is traditionally credited with initiating the modern custom of reading twice weekly in the synagogue. This reading is an obligation incumbent on the congregation, not the individual, and did not replace the reading by the king. The reading of the lot in the synagogue can be traced to at least about the second century B.C. when the grandson of Sirach refers to it in his preface as an Egyptian practice; it must, therefore, have existed even earlier in Judea.
The weekly Parashah is followed by a passage from the prophets referred to as a Haftarah. "Haftarah" does not mean "half-Torah. The word comes from the Hebrew root to mean "Concluding Portion." Usually, the Haftarah portion is no longer than one chapter and has some relation to the week's Torah portion.