Charlie D. answered • 08/03/20
Fourth-Year Chemistry Undergrad with Research Experience
Photons are the particles that light is made of.
Light has properties of both waves and particles. Originally, people thought that light was just a wave, so people referred to is an "electromagnetic wave" or "electromagnetic radiation". But only describing it as a wave led to some issues down the line.
To solve these issues people started using math that didn't describe light as just a wave, but described light coming in discrete particles (or packets of energy); which we named photons. Waves and particles are pretty different in terms of math/physics, but what is really important here is that particles cannot be divided into fractions: you can't have half an electron, half a proton, or half a photon.
So, photons are the indivisible chunks of electromagnetic radiation. This differs from the classical view which saw light as just a wave that you could break into any sized components interfering with one-another.
It could be helpful to look at the wikipedia article about the physics problems that started the particle point of view: the UV Catastrophe. I think the "Solution" section of the page is good to look at, even if you just ignore the two equations they put there.
