GAB stands for "genetic algorithm for bands". It involves repeatedly deforming the protein with randomly generated bands, then stabilizing and fusing the result. Groups of bands which improve the score are kept and "bred", and the process is repeated.
Rav3n_pl GAB v3.4.10 filter Cuts is a recent example of a GAB recipe.
A group of bands is called a "critter". Initially, the recipe generates a number of critters randomly. A generation of critters is referred to as a "herd".
Each critter in the herd is tested on the protein. Once testing is complete, the recipe creates a new herd. The new herd contains new critters creating by "breeding" the best critters from the previous herd. Breeding involves randomly combining bands from different critters. The recipe usually allows some "illegitimate" offspring of critters that were not among the best in the previous generation. The new herd may also include some new randomly generated critters.
The next herd is tested, and the process repeats for a specified number of generations.
Periodically, existing critters are wiped out, and a new herd made completely of random critters is generated.
The GAB strategy was derived from earlier "compressor" recipes, which used random groups of bands. Compressor recipes eventually offered an option to repeat groups of bands which improved the score, and the "repeat with variations" concept in GAB was a logical next step.