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''in mathematical logic''

A symbol of a [[formal language]] for denoting some fixed element (individual), a fixed operation or relation on some structure described by this language. In this connection one distinguishes between individual constants (cf. [[Individual constant]]), function constants and predicate constants. The set of constants of a language is called the ''[[signature]]'' of this language. For example, in one presentation, the signature of the language of formal arithmetic (cf. [[Arithmetic, formal]]) may consist of the individual constant  "$0$"  (zero), the two-place function constants  "$+$"  (addition) and  "$\cdot$"  (multiplication), the one-place function constant  "'$'$"  (successor) and the two-place predicate constant  "$=$"  (equality).



====Comments====
The term  "constant"  is also used for non-varying elements in all kinds of expressions, e.g. the constants of a polynomial (also called its coefficients, cf. [[Coefficient]]), field constants (when considering some construct over a [[field]], the elements of the field itself are often called constants), etc.

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