In Unity, “Terrain” refers to a “Component” used for creating a terrain such as a map.
* See the item of “Component”.
“Texture” refers to an image that lays over the surface of an object to give a visual effect. For example, wrapping an image of wood grain pattern around the surface of wood gives it more realistic texture.
“Toon Shading” refers to an expressive technique to create hand-drawn, cel animation-like effects on the screen.
It is sometimes called “cel shading” which is coming from “animation cels”.