Constructive Interference: When a crest and a crest or a trough and a trough meet together and the energies are combined
Destructive Interference: When a crest and a trough meet and the energies cancel out
Standing Waves: When interfering waves have the same amplitude and wavelength, the resultant pattern will remain nearly the same and there will be a nodal point which remains the same.
Noise-cancelling headphones emit the opposite wave of the incoming sound wave and the waves cancel out. (Destructive Interference)