A.P. stands for all purpose. The pattern was created by Denny Rickard of Oregon in the early 90's. It was used for copying the Damsel fly nymph on stillwater. I use it as a top fly nymph in larger sizes. It works well for me in May and June. I use the olive color in larger sizes like 8 and 10. It is very effective on the Rapid during the time when stoneflies and dragon flies are moving around during pre hatch.