Unity culling related technologies

Frustum Culling

Eliminate rendered objects outside the cone , Rejected objects will not be sent to GPU Render pipeline ( This is a Unity Operation at the level of shader The culling after vertex perspective division in is different ),Unity This technology is enabled by default .

Occlusion Culling

Eliminate those that are blocked by other objects , The camera is not visible ( But in the cone ) Rendered objects for . Use Occlusion Culling Manual setting required , And in Occlusion Culling Window Pass through Bake Calculate culled data .
https://docs.unity3d.com/Manual/OcclusionCulling.html

Occlusion Culling is different from Frustum Culling. Frustum Culling only disables the renderers for objects that are outside the camera’s viewing area but does not disable anything hidden from view by overdraw. Note that when you use Occlusion Culling you will still benefit from Frustum Culling.

Camera.layerCullDistances

For performance reasons, you might want to cull small objects earlier. For example, small rocks and debris could be made invisible at much smaller distance than large buildings. To do that, put small objects into a separate layer and set up per-layer cull distances using Camera.layerCullDistances script function.
https://docs.unity3d.com/ScriptReference/Camera-layerCullDistances.html

CullingGroup API

CullingGroup offers a way to integrate your own systems into Unity’s culling and LOD pipeline.The CullingGroup will calculate visibility based on frustum culling and static occlusion culling only. It will not take dynamic objects into account as potential occluders.
https://docs.unity3d.com/Manual/CullingGroupAPI.html