What is the difference between maximum and absolute shear stress in multi axial stress system?
given a tensor stress state you can find the shear on any arbitrary plane and direction. Maximum shear stress says we have found the plane with the maximum value. The maximum shear stress is always positive. (or zero for hydrostatic case) Note this is an invarient, you can report maximum shear without specifying a coordinate system.
absolute shear stress is probably the absolute value of the shear stress on a specified orientation which may or may not be the special orientation that gives the maximum. I say probably because the question hasn't given enough context, but I expect you are seeing something like
abs(sxy) in a given coordinate system