The phenomenon of superimposing of two waves such that the resultant wave have greater, lower, or the same amplitude.
There are two conditions for the interference.
Constructive wave interference: This type of interference occurs after adding of two maxima such that the amplitude of the resulting wave is equal to the sum of the amplitudes of individual waves.
Destructive wave interference: In this type of interference, the amplitude of the resulting wave gets reduced as the crest of one wave meets with the trough of another wave.