"Pattern" flying is one particular type of aerobatic flying. It was originally named that because the competitions were set up so that the flyers in different skill levels all flew the same pattern of maneuvers for their skill level. Originally, the classes were A, B, and C, and eventually D. Classes C and D had novice and expert divisions. Class C was the top level, and D was the FAI or international pattern.

Over the years, the maneuvers have changed greatly, and the classes have been renamed. Of course, the design of the aircraft has also changed, as the types of maneuvers flown and the overall pattern has changed. When you have a competition with fixed parameters, you can expect the designs of the models to change so that the models are best-suited to perform well in that particular type of competition.

You can find more by going to the Pattern forum here on RCU.