Orthodox Judaism is a collective term for fundamentalist branches of contemporary Judaism. Theologically, it is chiefly defined by regarding the Torah, both Written and Oral, as literally revealed by God on Mount Sinai and faithfully transmitted ever since. Orthodox Judaism therefore advocates a strict obedience to religiously originated laws.
Roughly, it may be divided between Haredi Judaism ("ultra-Orthodox") and "Modern Orthodox Judaism", which is somewhat more open to outer society. Each of those is itself divided into different movements. These movements are almost uniformly exclusionist, regarding their own view as the only authentic form of Judaism and rejecting all competing non-Orthodox philosophies as illegitimate.
The term "Orthodox Judaism" itself (with "Orthodox" meaning "righteous/correct opinion") can be seen as another example of double standards regarding Judaism, avoiding the often negatively perceived term "fundamentalist", which is frequently applied to other religious movements, especially Christian movements, with claimed strict literalism regarding holy texts.