It is a shading, as well as a rendering tool to calculate the exposure of each element in a scene to ambient lighting. It is efficient and straightforward to use this technique as ambient occlusion simulates the shadow, which emerges by objects that are blocking the ambient light.
The ambient light is environmental as against other types of lighting effects, this occlusion does not refer to the direction of the light.
It is a kind of light that is present in a scene before adding other types of lightning. It is mostly natural light in the virtual environment. It can be light coming from the outdoors or windows. This light does not have a specific direction. It is not possible to use it to cast shadows. It is the most essential for photographers or video makers. Because most of the shots depend on this kind of light.
The extended version of this acronym is screen-space ambient occlusion. It is not as popular as the other types of occlusions. However, it all depends on the game developers. Its effect significantly changes from game to game. The most crucial point is the professionalism of game creators to use it properly.
It is horizon-based, but the other one is high-definition ambient occlusion. Both of them offer a high-quality effect on graphic cards. However, game developers do not use it so much as they use SSAO. There is also a recent term VXAO, meaning voxel ambient occlusion effect, and only graphic processor units can benefit from it. It is a successor's unique effect on HBAO. It is a more demandable kind of effect which requires high-quality programs and knowledgeable professionals to use to create the product for screens.