Answer:
Diffraction and Interference
Explanation:
The light sometimes acts like a particle and sometimes like a wave, yet the diffraction and interference are proof of the light's wave nature.
First of all, as a definition, the interference is an effect caused by superposition of two systems of waves (from two different sources). (As an example, the interference -distortion- in radio waves)
The diffraction, by the other hand, refers to several events that occur when a wave meets an obstacle. (usually described as a bending of waves around obstacles -likethe water waves- and in other cases as the dissemination of waves, once they passed small openings)