The Knightfall Protocol was the last of Batman's backup plans, to be deployed only when his secret identity was compromised in order to protect those closest to him. It was unknown when Batman devised that final contingency plan. The protocol involved faking Batman and Alfred's deaths through the destruction of Wayne Manor via explosives planted to destroy the mansion and the Batcave while keeping the explosion within the gates of the manor. The Knightfall Protocol was finally deployed during the events of Batman: Arkham Knight after Scarecrow revealed on television that Bruce Wayne was Batman to Gotham City and possibly, the world. After he neutralized Scarecrow with his own Fear Toxin, imprisoned all of his worst enemies for good, Batman unmasked in front of the Batsignal, took the Batwing and the Batmobile to Wayne Manor before he triggered the explosives in front of hundreds of news reporters, and brought the legend of Batman to an end.
The Knightfall Protocol was likely named after the Knightfall story arc of the Batman comics, though it has little in common in terms of a plot device.