What is Belief?

Legal Definition
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
Legal Definition
The conviction of the mind, arising from evidence received, or from information derived, not from actual perception by our senses, but from. the relation or information of others who have had the means of acquiring actual knowledge of the facts and in whose qualifications for acquiring that knowledge, and retaining it, and afterwards in communicating it, we can place confidence. " Without recurring to the books of metaphysicians' "says Chief Justice Tilghman, 4 Serg. & Rawle, 137, "let any man of plain common sense, examine the operations of, his own mind, he will assuredly find that on different subjects his belief is different. I have a firm belief that, the moon revolves round the earth. I may believe, too, that there are mountains and valleys in the moon; but this belief is not so strong, because the evidence is weaker." Vide 1 Stark. Ev. 41; 2 Pow. Mortg. 555; 1 Ves. 95; 12 Ves. 80; 1 P. A. Browne's R 258; 1 Stark. Ev. 127; Dyer, 53; 2 Hawk. c. 46, s. 167; 3 Wil. 1, s. 427; 2 Bl. R. 881; Leach, 270; 8 Watts, R. 406; 1 Greenl. Ev. ยง7-13, a.
-- Bouviers Law Dictionary
Legal Definition
A conviction of the truth of a proposition, existing subjectively in the mind, and induced by argument, persuasion or proof addressed to the judgment. Kelier v. State, 102 Ga. 506, 31 S. E. 92. Belief is to be distinguished from "proof," "evidence," and "testimony." See Evidence. With regard to things which make not a very deep impression on the memory, it may be called "belief." "Knowledge" is nothing more than a man's firm belief. The difference is ordinarily merely in the degree; to be judged of by the court, when addressed to the court; by the jury, when addressed to the jury. Hatch v. Carpenter, 9 Gray (Mass.) 274. The distinction between the two mental conditions seems to be that knowledge is an assurance of a fact or proposition founded on perception by the senses, or intuition; while belief is an assurance gained by evidence, and from other persons. Abbott.
-- Black's Law Dictionary
Legal Definition
The ideas true to a party that believes it.