What does a material define in a Unity game object?

A material in Unity primarily defines the visual properties of a GameObject, which includes aspects such as color, texture, and how light interacts with the surface. When applied to a GameObject, the material determines how that object appears in the game environment. It can influence the object's surface properties like shininess, transparency, and texture mapping, which are crucial for creating visually appealing scenes.

For example, different materials can make a surface appear metallic, glassy, or matte, providing developers with the tools to convey different aesthetics and atmospheres in their games. This visual definition is essential because it affects how players perceive objects and environments, contributing significantly to the overall gaming experience.