 In a formal system a symbol may be used as a token in formal operations.The set of formal symbols in a formal language is referred to as an alphabet (hence each symbol may be referred to as a "letter")

A formal symbol as used in first-order logic may be a variable (member from a universe of discourse), a constant, a function (mapping to another member of universe) or a predicate (mapping to T/F).Formal symbols are usually thought of as purely syntactic structures, composed into larger structures using a formal grammar, though sometimes they may be associated with an interpretation or model (a formal semantics).