Abs Vector produces absolute values across the X, Y and Z components, effectively making each a positive number by negating the negative values.
This example uses a colour/vector source that produces positive and negative values in the three X,Y,Z directions. Vectors may have values greater or lower than the visible range of 0 to 1, hence the black areas in the top preview panel. This pattern is then used as a vector displacement map which in turn displaces a Plane Object to show displacement in three directions.
When we insert an Abs Vector node, all negative values become positive.
If there's any errors, omissions or questions about the above, please leave a comment and we will add further details in this post when relevant.
https://planetside.co.uk/wiki/index.php?title=Abs_Vector