The name comes from the Hebrew word Torah, which literally means instruction. The is the instruction which Allah gave to the Jews through the Prophet (pbuh). The revelation of (pbuh) contains five books or sections as follows: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. Collectively, these five are also called the Pentateuch, a word of Greek origin meaning "the five-fold book."
However, the instruction given to the Jews did not end with Prophet (pbuh). Well-known prophets followed in 's footsteps including Prophet , , , , and many others (peace be upon them all). Their writings are collected here along with all the instruction given to the Jews that started with (pbuh). As a result, altogether they are called the , the revelation given to the Jews, as the following verse says, "It was we who revealed the : in it is guidance and light. By its standard the Jews have been judged, by the prophets who submitted to Allah's will..." (Quran, Surah 5:44).
Today this collection is often called the Old Testament by Christians. The Jews call it the Tanakh, which is a brief way of referring to the TAurat, the NAbhim, and the KHetubim (the Law, the Prophets, and the Writings). Here we simply call it the holy , that is, the instruction given to the Jews.