A probability amplitude is a complex number that describes the behavior of quantum mechanical systems.
Image of the probability amplitude of electron for hydrogen atom...
Max Born
In 1926, Max Born proposed that there is a relationship between the quantum state vector of a system, with results of the observation of that system.
Interpreting values of the wave function as a probability amplitude is a pillar of the Copenhagen interpretation of quantum mechanics.
Born won the Nobel Prize in 1954 for this work. The probability thus calculated is known as the "Born probability."