The Many-Worlds interpretation is a theory in quantum mechanics that suggests every possible outcome of a quantum event actually occurs in its own separate universe. This means that when a particle is observed, it doesn't just take one path; instead, all potential paths happen simultaneously, creating a vast number of parallel universes. This interpretation was first proposed by physicist Hugh Everett III in 1957. It challenges the traditional view of quantum mechanics, which relies on the idea of wave function collapse. In Many-Worlds, the wave function never collapses; instead, it branches out, leading to an infinite number of realities.