Specularity

Do you know how when you look at something shiny, sometimes you see your reflection? This is called "specularity". It happens because of how the surface of the shiny thing is shaped and how light bounces off of it.

So, imagine you have a really bumpy surface, like a rock. If you shine a flashlight on it, the light bounces off in all different directions because of all the bumps. But if you have a very smooth surface, like a mirror, the light bounces off in the same direction as when it hit the mirror. This is why you can see your reflection in a mirror.

And that's what "specularity" means - it's about how much light reflects off of something in the same direction it came from. So, the more specular something is, the shinier and more mirror-like it will be.