Prism is a piece of glass or other transparent material. The precise angles and the plane faces are used to analyze and reflect the light.
A triangular prism is used to separate the white light into its constituent colors, which is known as a spectrum.
Lights with different wavelengths refract in different amounts. For example, the light with a shorter wavelength (like violet) refracts or bents the most, whereas the light with a longer wavelength (like red) refracts or bents the least.
This separation of the light spectrum into different colors is known as the dispersion of light.