"Law" is from nomos (νόμος) which means in Greek "anything assigned", "a usage", "custom", "law", "ordinance," or "that which is a habitual practice." It is the basis of the English words "norm" and "normal." This word, however, was not used by Jesus to refer to civile laws, that is, the Roman laws of the time.
However, to Jewish used this word to describe the books of Moses, known the Torah ("Instruction"). Moses was considered the law-giver as well as a prophet. The Jewish term Torah is from a root that means "to guide" and "to teach."
The books of the law include:
Is Jesus always referring to these books when he say "the law?" Looking at all the verses in which Jesus used the Greek word nomos, this seems to be the case. Notice how often he refers to "what is written."