If a geometry is hidden behind another geometry that geometry which is hidden can be culled away is known as occlusion culling.
The idea behind efficient occlusion Culling algorithms is to perform some simple tests early on to cull sets of hidden objects. In a sense, backface culling is a simple form of occlusion culling.
There are two major forms of occlusion culling algorithms, namely point-based and cell-based.
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Point-based visibility is just what is normally used in rendering, that is, what is seen from a single viewing location.
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Cellbased visibility, on the other hand, is done for a cell, which is a region of the space containing a set of viewing locations, normally a box or a sphere. An invisible object in cell-based visibility must be invisible from all points within the cell.