Foggins comes in handy because you can fade out what is in the distance and so you dont seen the scene and models popping up as you moves towards them

a clipping plane decideds what Models can be scene at a certant range when the models come into the range they appear

Volumetric fod is considered an object. it is a cloud of fog chaging as you move into and that you can pass through and come out on the other side 

A Read-Modify-Write operation is wen for example fog needs to be renderd in the game the fog needs to be transparant so you have to get the pixels behind it mix in the fog and then put the gblended pixel in its place

 There are two different blend modes one is Straight Aplha blending this addes a percentage of the background pixel to the one infront of it

another way of blending is Additive blending which takes a percentage of an old pixels and addes a specific of the new pixel