Diffraction of electromagnetic waves deals with the way light bends around the edges of obstacles into regions that would otherwise be in shadow.
Interference deals with the way that electromagnetic waves behave during the diffraction process.
Diffraction can be produced by the edges or by a hole (aperture) in any opaque surface or object.
Diffraction causes a propagating electromagnetic wave to produce a distinctive pattern as waves interfere with one another. The resulting pattern becomes visible if diffracted light subsequently strikes a surface.