Constant

Constant is:

Physical constants, physical quantities, which are regarded as universally valid and immutable
Constant ( logic), a logical expression with invariable meaning
Constant ( programming), an invariable during the duration of the program value
Constant ( fraternity ), a meeting room of a frat

Mathematics:

Mathematical constants, specific, real, non- integer, which is of particular interest in mathematics
A specific element of a mathematical structure or equivalent a zero binary operation, see link (mathematics) # zero digit shortcuts