They embrace dualistic, black-and-white, absolutist thinking. Everything and everyone is either good or evil.
They fear annihilation.
They take their values from an idealized past, either real or imagined.
They often withdraw from mainstream society to form their own communities and cultures.
They see themselves in a struggle to retake society and reinstate whatever they think the modern world is destroying.
The point is that people can be deeply and traditionally devout without being fundamentalist. Belief in God or Allah or the Pure Land is not in itself fundamentalist. Investing scripture with sacred authority is not necessarily fundamentalist. A traditionally religious person who is open to new understanding and tolerant of other views is plainly not a fundamentalist.