A belief is a firm thought that something is true, often based on revelation. Belief is usually a part of belonging to a religion. It is different to scientific knowledge that can be tested, but belief is not able to be tested. For example, a person may believe in God or gods. The word is also used to describe what a person expects will happen based on limited information. For example, "I believe Amy will come around today". Belief is also something you believe in but you cannot prove exactly.