Scientists refer to plate tectonics as a theory. what is a theory? how is plate tectonics a theory? why isn't continental drift considered a theory?

A theory is an explanation of some aspect of the natural world that has been substantiated through repeated experiments or testing. Plate tectonics is a theory because it provides an explanation of why and how segments of the earth move and cause earthquakes and mountains and volcanos. Continental drift isnt considered a theory b ecause Wegener's idea of continental drift is a hypothesis. He doesn't have concrete proof of it.