WAVE PARTICLE DUALITY
Phenomena such as Interference, Diffraction and Polarisation can be explained by wave theory of light, however, phenomena such as photo electric effect and Compton effect can be explained by particle theory of light.
According to Planck Quantum Theory emission and absorption of light is not continuous but it is discrete and light is in form of small bundles or packets of energy which is called Photons. Hence light behaves as a wave on one hand and a particle on the other hand. This nature of light is known as dual nature and this property of light is known as Wave-Particle Duality.
On the basis of this dual nature of light, De-Broglie suggested that dual nature is not only of light but each moving material particle has dual nature. He assumed a wave to be associated with each moving material particle which is called the "Matter Wave".