Wave function is a fundamental concept in quantum mechanics that describes the probability amplitude of a particle being in a certain state. It is a mathematical function that encapsulates all the information about the particle's position, momentum, and energy. The wave function is used to calculate the probability of finding a particle in a particular location or state when measured. It plays a crucial role in understanding the behavior of quantum systems and is essential for predicting the outcomes of experiments at the atomic and subatomic level.