The Torah is the Hebrew name of the first five books of the Bible: Genesis, Exodus, Leviticus, Numbers and Deuteronomy. Both Jews and gentiles often refer to this collection as the Pentateuch (Greek: "five books"). The Torah is considered canonical in the Jewish, Catholic and Protestant Bible. Another name for the Torah is Chumash (a Hebrew word).
The Samaritans have their own version of the Torah, which contains many variant readings. Many of these agree with the Septuagint against the Massoretic Text, leading many scholars to believe that parts of the Samaritan text may have once been common in ancient Palestine, but rejected by the Massoretes.
The law of most Jews is not directly from the laws in these books; rather, most Jews follow the traditional explication of these laws that can be found in the Mishnah and in the Talmud. (Karaites, who reject the oral law, are a major exception.)
According to Jewish and Christian tradition, these books were dictated by God to Moses on Mount Sinai, and constitute a word-for-word transcription of God's words. Modern day scholars point out that the text of the Torah appears to be redacted together from a number of earlier sources; this is known as the documentary hypothesis; see JEDP theory.