What are the fundamental differences between the Jewish Torah and the Old Testament?
Strictly speaking, as the word “Torah” means “Law”, the books of the Torah are the first five books of the Bible. Genesis, Exodus, Leviticus, Numbers, Deuteronomy.
However, besides using Torah in this sense, and in its strict sense to mean the Jewish Law itself, Jewish people also use it more loosely to refer to the whole Jewish Bible.
The Jewish Bible, which is our Old Testament in a different order, is also called by them the “Tanakh” which is a Hebrew acronym for Torah, N’vi’im, K’tuvim: the Law, the Prophets, and the Writings. (TaNaK)
There are some differences between the names of the books, and some smaller books are collapsed into collections, and there are a few differences in chapter and verse numberings, but essentially, the Torah (in the sense of the Tanakh) and our Old Testament contain the same text.
However Christians are generally better off using the word Torah to refer solely to the first five books, and adopting the Jewish practise of referring to the whole Jewish Bible as the Tanakh if conversing with Jewish people.