Born's rule

in quantum mechanics, the rule that the probability of observing an eigenvalue is the square of the modulus of the inner product between the quantum state and the eigenstate corresponding to the eigenvalue

Born's rule (also called the Born law, Born's rule, or Born's law) is a law of quantum mechanics. It is named after its originator, the physicist Max Born. The Born rule is one of the key principles of quantum mechanics.

It gives the probability that a measurement on a quantum system will yield a predicted result.