Light may be one of the first things humans ever discovered, but that doesn’t mean we fully understand it. In fact, light has some properties that we are still unable to fully understand.
As we have discussed, matter is made out of atoms, and atoms are made out of protons, neutrons, and electrons. A beam of light is a little bit different. Light is made out of photons, so when you hold up a flashlight, photons are beings sent out of the flashlight to illuminate the room. As they travel through air, they can hit things and bounce of (reflection) or they can travel through some items, like glass, and change direction (refraction).
How photons travel is still a mystery to scientists. Sometimes photons travel like particles. But sometimes light travels like waves. Often we see light doing both at the same time.
But sometime light can shine slightly behind an object, which is impossible for particles to do. We call this light duality, as a way to explain how light can be both particle and wave.