What is a parity generator in physics?

Parity has a different meaning in physics than in electronics. In electronics it is about whether the sum of a set of bits is even or odd. In physics it deals with symmetry under mirroring operations.

Parity is a symmetry for many (but not all) physical laws: if $x$ is replaced by $-x$ then the behaviour under the physical law is the same. Depending on whether an object is invariant or changes under mirroring one can speak about its parity. This property depends on the type of object (typically its spin) rather than some state of the object.