Wave-particle duality is a fundamental concept in quantum mechanics that describes the dual nature of particles, such as electrons and photons, which exhibit both wave-like and particle-like properties.
When particles are observed in certain experiments, they exhibit behaviors similar to waves. This includes phenomena such as interference and diffraction, which are typically associated with waves.
On the other hand, in other experiments, these same particles exhibit behaviors that are characteristic of particles, such as the ability to be localized at a specific position and the ability to carry momentum and energy like a particle.