Hi I am a student who just started using Unreal Engine and I have seen some examples of Shaders using Absolute World Position but I have a hard time having a clear understanding of what it is. In the UE4 documentation it’s says it’s often used to calculate the radial distance of the camera to a pixel.
Does it mean it calculates the distance between where you are in the world and the exact pixel the camera is on?..
Sorry if I am unclear,I am new to this, thanks for your time!
can anyone answer this question? I’m stuck here too 
its the position of the surface in world space. if you were to subtract world position from the location of the camera then get the length of that vector it would give you the distance to that surface. but on its own its just the coordinate of that pixel in world space. for example if you have a vert at the center of the world its world position would be 0.0.0. hope that helps.
its worth mention that this can be used for all sorts of things so if your looking at examples it might seems confusing. its common to use it to make world based uv for ground and wall textures among many other things. if your interested in this sort of thing i would recommend looking into vector math or simply having a look at the great examples in the math hall example level.