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