Depends on who is asking and why. I would just say that there is a fundamental code of Jewish observance, the Torah, but just as some people like chocolate and some people like vanilla, some Jews have certain customs that differ from others, but all are within the bounds of the fundamental Jewish law from the Torah.
If they are talking about Orthodox, Conservative, Reform, then the answer is that the Torah teaches us fundamental precepts and requirements of religious behavior within our daily lives, and some Jews follow all or most of these laws as they were passed down through the generations, and some do not.