This principle states that all matter and radiation exhibit both wave-like and particle-like properties. It's a fundamental concept in quantum mechanics, challenging the classical view of physics where things were strictly defined as either waves or particles.

Here's a breakdown:

* Wave-like properties: Refer to phenomena like diffraction and interference, where light or matter behaves like waves.

* Particle-like properties: Refer to phenomena like the photoelectric effect, where light interacts with matter as if it were composed of discrete particles called photons.

The wave-particle duality is not just a theoretical concept, but it's been experimentally verified for various phenomena involving light, electrons, atoms, and even larger molecules. This duality has revolutionized our understanding of the fundamental nature of reality.