ELI5: Explain Like I'm 5

Photon

A photon is a tiny particle of light. Photons are measured in 'wavelengths' which are like the sizes of different kinds of light. Photons travel in a straight line and can move incredibly fast, faster than anything else in the universe! They carry energy from one place to another, usually from the sun to things on Earth. The energy from the photons is what makes things seeable or sometimes invisible!