▪ a set of principles on which the practice of an activity is based: "a theory of education"
▪ an idea used to account for a situation or justify a course of action: "my theory would be that the place has been seriously mismanaged"
▪ a collection of propositions to illustrate the principles of a subject.
Word Originlate 16th century (denoting a mental scheme of something to be done): via late Latin from Greek theōria ‘contemplation, speculation’, from theōros ‘spectator’.