From China Digital Space
Belief is the state of mind in which a person thinks something to be the case, with or without there being empirical evidence to prove that something is the case with factual certainty. Another way of defining belief sees it as a mental representation of an attitude positively oriented towards the likelihood of something being true. In the context of Ancient Greek thought, two related concepts were identified with regards to the concept of belief: pistis and doxa. Simplified, we may say that pistis refers to "trust" and "confidence", while doxa refers to "opinion" and "acceptance". The English word "orthodoxy" derives from doxa. Jonathan Leicester suggests that belief has the purpose of guiding action rather than indicating truth.
In epistemology, philosophers use the term "belief" to refer to personal attitudes associated with true or false ideas and concepts. However, "belief" does not require active introspection and circumspection. For example, we never ponder whether or not the sun will rise. We simply assume the sun will rise. Since "belief" is an important aspect of mundane life, according to Eric Schwitzgebel in the Stanford Encyclopedia of Philosophy, a related question asks: "how a physical organism can have beliefs?" (Wikipedia)