Moving pictures? (2,3)
(Other definitions for op art that I've seen before include "Illusory graphic work" , "Sixties movement" , "Abstract visual style for the 1960s, giving the illusion of movement" , "Abstract geometrical genre of painting" , "Illusory graphic style" .)
(Other definitions for piecrust that I've seen before include "that blackbirds escaped from" , "Baked pastry top" , "Pastry on dish" , "pastry toppings" .)