Invariant may have several meanings, among which are:

• Invariant (computer science), an expression whose value doesn't change during program execution
• In computer science, a type in overriding that is neither covariant nor contravariant
• Invariant (mathematics), something unaltered by a transformation, like for example: taking a homotopy group functor on the category of topological spaces. Then, homomeomorphic spaces have isomorphic fundamental group. See topological invariant.
• Invariant (music)
• Invariant (physics) a quantity conserved by system symmetry
• Invariant representation (cognitive science), the form or essence of something, an abstraction from particulars
• The Invariant Society, the undergraduate mathematical society of Oxford University