A parashah (Hebrew: פָּרָשָׁה (Pārāšâ) "portion," plural: parashot or parashiyot) formally means a section of a biblical book in the masoretic text of the Tanakh (Hebrew Bible). In the masoretic text, parashah sections are designated by various types of spacing between them, as found in Torah scrolls, scrolls of the books of Nevi'im or Ketuvim (especially megillot), masoretic codices from the Middle Ages and printed editions of the masoretic text.
The division of the text into parashot for the biblical books is independent of chapter and verse numbers, which are not part of the masoretic tradition. Parashot are not numbered, but some have special names.
The division of parashot found in the modern-day Torah scrolls of all Jewish communities is based upon the systematic list provided by Maimonides in Mishneh Torah, Laws of Tefillin, Mezuzah and Torah Scrolls, chapter 8. Maimonides based his division of the parashot for the Torah on the Aleppo Codex. The division of parashot for the books of Nevi'im and Ketuvim was never completely standardized in printed Hebrew bibles and handwritten scrolls, though important attempts were made to document it and create fixed rules.
Incorrect division of the text into parashot, either by indicating a parashah in the wrong place or by using the wrong spacing technique, halakhically invalidates a Torah scroll according to Maimonides.
Read more about Parashah: Purpose of The Section Divisions, History of The Section Divisions, Spacing Techniques, Parashot in The Torah, Parashot in Nevi'im, Poetic Layout of Psalms, Proverbs and Job, Parashot in Ketuvim, Songs With Special Layout