The term 'Gangrene' usually describes 'Dry Gangrene', the condition where a portion of the body dies from lack of blood supply or from being in some other way non-viable.  This is a serious condition that usually results in loss of a toe, part or all of the foot, or part or all of the leg.

The most common causes of gangrene are diminished circulation from diabetes, smoking, vascular disease, blood clots, infection and frostbite. 

Gangrene makes the affected tissue looks black, but as several other conditions can make tissue look black--moles, bruising, melanoma, e.g.--it is important that the proper diagnosis be made.

The most common treatment for gangrene is amputation of the affected tissues, though antibiotics are sometimes used to treat any associated infection associated with the gangrenous, dead, tissue. 

The term 'Gas Gangrene',  in contrast, is used to describe a severe, rapidly-advancing, limb-threatening or even life-threatening infection that produces gas in the tissues that's visible on X-ray. 

Gas gangrene is an urgent medical condition that is treated as an emergency situation, as it can put the patient's very life in jeopardy. 

Gas gangrene is treated with intra-venous antibiotics and aggressive surgery to drain the infection and remove non-viable tissues.