Tissue death. It is tissue death due 2 no blood supply 2 meat the extremities needs. It can b dry meaning no infection & if it's a finger or a toe, it can just die & fall off. Wet means that infection is present an needs amputation so u do not become septic. Also a vascular procedure can b done 2 get better blood supply 2 the extremity, & hopefully prevent further loss of limb or digits. The dead tissues=black.