An educated guess is a guess in which you take into account factors which might affect the outcome using reason. It is a term used to clarify that a guess is not one which is made “off the top of your head”—that is, guessing the first possibility that comes to mind—but rather one which, although it is still a guess, is generated by considering multiple possibilities and selecting the one thought most likely by considering those factors that a reasonable person might assume will affect the outcome.