What is the difference between orthodox and reform judaism?

Orthodox Jews believe that the Torah must be fully observed. They keep the laws of Judaism as codified in the Shulchan Arukh (Code of Jewish Law), which lists the laws of the Torah and Talmud. Torah-study is seen as very important; and the modern world is seen as subservient to the Torah, not the other way around.
Other Jewish groups (Conservative, Reform) adapt or change the Torah-laws in contemporary life, to a greater or lesser degree.