Torah comes from the Hebrew word for "law" and refers to the first five books of the Bible: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy—also known as the Pentateuch. The word torah is used also to refer to the scroll of parchment on which the Pentateuch is written. The scroll is considered a sacred liturgical object in synagogues and is often richly decorated and given other marks of respect. In Orthodox Judaism, the Torah also can refer to the entirety of the law, both in written form (Scripture and other sacred writings) and in oral Tradition.
When we as Catholics refer to the Old Testament, we are referring to all forty-six books of the Bible written before Christ, including the first five that the Jews call the Torah.