A belly gun is a short-barreled revolver, for concealed carry. It may have additional, distinctive features: shortened grip frame, absent front sight, de-spurred ("bobbed") hammer, absent front half of the trigger guard, and large (.44 or .45 inch) caliber.
The origin of the term is obscure, but the belly gun's modern formulation dates from the first half of the Twentieth Century, and can be attributed to a small group of men, most with military backgrounds: Colonel Rex Applegate, Major Eric A. Sykes, Lieutenant-Colonel William E. Fairbairn, pistolsmith John H. Fitzgerald, and perhaps most prominently Colonel Charles Askins. In 1939, Askins wrote, "The grandest defense gun I have ever had was a Colt .45 New Service with the barrel cut down to two inches. The hammer had been dehorned ... the trigger guard was cut entirely away in the front ... the grip was shortened ... it was a whiz for the purpose intended."[1]
The term "belly gun" may have arisen from the practice of carrying of the weapon tucked into the waistband, close to the belly. However, others[2] think the term instead comes from the envisioned mode of employ for these guns: firing from extremely close-range into the belly of an opponent.
Belly guns, as described above, would be most suited to use at close range, as a defensive weapon of last resort. The "Fitz Special," a revolver modified as described above, was the innovation of John H. Fitzgerald.