Wave function collapse is a concept in quantum mechanics that describes how a quantum system transitions from a state of multiple possibilities to a single outcome when measured. Before measurement, a particle, like an electron, exists in a superposition of states, meaning it can be in multiple positions or conditions at once. When an observation is made, the wave function collapses, and the particle assumes one specific state. This phenomenon is crucial for understanding how quantum systems behave and is often illustrated using thought experiments, such as Schrödinger's cat. In this scenario, a cat in a box is simultaneously alive and dead until someone opens the box and observes it, demonstrating the principle of superposition and the effect of measurement on quantum states.