Phases - different states (determined by time and space coordinates) a body goes through while oscillating
Frequency - number of complete oscillations per one second
Refractive index of a medium is the ratio of speed of light in vacuum and speed of light in that medium
Diffraction grating is a device used to produce optical spectra and to measure wavelengths.
Diffusion is the mixing of the atoms or molecules of one substance with those of another
Osmosis is the gradual spread of a liquid through a solid part of sth