THEORY

Webster's New World Dictionary: 

theory  [from French theorie < Late Latin theoria < Greek theoria, a looking at, contemplation, speculation, theory]  2 a speculative idea or plan as to how something might be done  3 a systematic statement of principles involved [like Einstein's Theory of Relativity]   4 a formulation of apparent relationship or underlying principles of certain observed phenomena which has been verified to some degree

We'll be using the meaning of "theory" as defined in #4 above.  In a sense, essays are informal explanations of our theories about "things."