Orthodox Judaism can be seen as a more traditional form of Judaism while Reform Judaism, on the other hand, is most definitely an updated and modernized form of Judaism.
Orthodox Judaism keeps a very firm emphasis on upholding the law. For example, all dietary restrictions are maintained and men and women do not sit together during worship. This is in keeping with the Orthodox determination to retain as much as possible of the Talmud and Torah.
By contrast, Reform Judaism holds that it is really only the moral teachings of the Torah that must be obeyed. The rabbinic teachings about things like diet and ceremonial purity need not be obeyed. This is a much less traditional approach to the Jewish faith.