Individual constant

object constant

A symbol of a formal language used to denote a distinguished, fixed element (individual) in the structure described by this language. Every individual constant can be regarded as a $0$-place function constant. For example, the language of field theory contains the two individual constants 0 and 1, while the language of projective geometry contains no individual constants at all.

References

[a1]	J.L. Bell, M. Machover, "A course in mathematical logic" , North-Holland (1977)