Interference in physics is a phenomenon that occurs when two or more waves meet while traveling along the same medium. When two waves overlap, they can either add up or partially or entirely cancel each other, depending on the alignment of their peaks and troughs. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.

There are two types of interference: constructive interference and destructive interference. Constructive interference occurs when two waves have a displacement in the same direction, resulting in a greater displacement of the medium than the displacement of the two interfering pulses. Destructive interference occurs when two waves have a displacement in the opposite direction, resulting in a smaller displacement of the medium than the displacement of the two interfering pulses.

Interference is a fundamental concept in physics and is observed in various fields, including optics, acoustics, and quantum mechanics. In optics, interference of light is a unique phenomenon in which we can never observe superposition of the electromagnetic field directly. Instead, we infer the presence of interference by observing the pattern of alternating dark and light bands caused by intensification and extinction at points where the waves are in phase and out of phase, respectively.