Parity is both an operation and an intrinsic property used to describe particles and their wavefunctions (mathematical representations of one or more particles) in quantum mechanics (a branch of physics focusing on particles smaller than an atomic nucleus).

The parity operation is a combination of a left-right trade (mirror reflection) with a top-bottom switch. This combination is also called a spatial inversion. How objects behave under a parity operation defines their intrinsic parity. All microscopic particles have an intrinsic parity that helps us tell them apart. An object or group of objects that is the same before and after a parity operation is called parity invariant. A parity invariant object has 'even' or '+1' intrinsic parity. If the parity of an object changes due to a parity operation, it has 'odd' or '-1' intrinsic parity.

Even though people do not obey reflection symmetry (their right and...