Ambient Occlusion

Keywords: AO

Ambient Occlusion is a an approximation of how much light would hit a surface without taking a specific light direction into account. Meaning that tight crevices, folds and other creases would get darker than an area exposed to a lot of light.

This approximation can be used as a mask for various different effects like dirt or wear. It's often baked offline and used as vertex color or a texture. From a consumer point of view it's seen a bit differently as it's often used as a post effect to add contrast to the scene.