Can you please explain the significance of photoelectric effect?

The photoelectric effect is the emission/removal of electrons, normally, from the surface of a metal. This is done as light is shone on the metal. This is a very useful proof that light can act as a particle, due to the fact that there is a threshold frequency, above which the photoelectric effect only works. The threshold frequency is the lowest frequency at which enough energy(known as the work function) is provided to the electron so that it can be removed from the surface of the metal. This proves that light behaves as a particle as it is evidence that the interaction between the photons of light and the electrons is one to one. Otherwise, if light could only behave as a wave, the photoelectric effect would occur regardless of the frequency of the light, and only have different time delays.