What is a Glock pistol gap?

"GAP" when referring to Glock refers to a caliber. A few years ago, Glock designed the .45 GAP (which stands for "Glock Auto Pistol" as a way to get a .45 caliber cartridge in a smaller frame gun. It was a failure. There is nothing wrong with the cartridge, but it just doesn't do much the .45 ACP won't do.