Constructive Interference:
Is when 2 crests that come from different sources meet, this causes the energies to combine and displace the medium.
Standing Wave
Is when there are 2 or more waves (that have the same amplitude and wavelength), this allows the pattern to remain almost stationary. Can also be referred to as a standing wave interference pattern.
Destructive Interference:
Is when the crest and trough meet out of phase, making their energies, ultimately, work against each other or cancel each other out.