How the ideas connect
A good science page should make the connection visible, not just list definitions.
Waves
A wave is a propagating disturbance that can transfer energy and information without requiring a net transport of matter over the same distance.
Frequency, wavelength and propagation speed are linked; what oscillates locally depends on the kind of wave and its medium.
Interference
When coherent waves overlap, their amplitudes combine. Depending on phase, the result can be reinforcement, cancellation, or anything between.
Interference turns phase differences into observable intensity patterns and lies behind interferometers, thin-film colours and many precision measurements.
Diffraction
Diffraction is the spreading and restructuring of a wave when it encounters an aperture or obstacle whose dimensions are relevant to its wavelength.
It is not a defect of waves: it is one of their signatures, and it ultimately limits the resolving power of optical instruments.
Refraction of light
When light crosses between media, its propagation speed changes and its direction generally changes as described by Snell’s law.
Frequency remains fixed across a stationary boundary while wavelength changes with propagation speed.
What to notice
A good science page should make the connection visible, not just list definitions.
Sources
IUPAC Gold Book · NIST · BIPM