A Rational Fic is one which makes a deliberate effort to reward a reader's thinking. It's the opposite of Bellisario's Maxim. The Worldbuilding is intended to stand up to careful thought; the plot is driven by characters or circumstances that themselves are part of the story, the heroes generally think clearly (in ways the reader can follow), and a clever reader can deduce what's hidden or what's coming. Very often, the fic is also intended to teach the reader something about rationality.
One of the first authors to use aspects of rational thinking and non-Aristotelian logic
as the basis of their world-building and character interactions was A.E. van Vogt, specifically in the Null-A series. In its modern form, the genre was popularised by Harry Potter and the Methods of Rationality, so most self-described "rational" stories are posted online. Because of this, the name uses Fic instead of fiction; some fans use the terms Rational Fiction, Rationalist Fic, and Rationalist Fiction interchangeably, though most use Fiction for published/non-derivative works, and Rationalist for works that not only aim for realistic intelligence, but try to teach principles of rationality. A sizeable community of people who write or enjoy this type of fiction exists on Reddit.
The genre can in some respects be thought of as a type of Science Fiction in which the sciences are things like game theory, bayesian reasoning, cognitive psychology, behavioral economics, social choice theory, information theory, computation, complexity, epistemics, memetics, and other fields that relate to the way we form beliefs, make decisions, or solve problems in general.
Also see Competence Porn, which might be the reason why rational fics are popular. Might devolve into a Philosophical Parable, if rationality as an ideology or philosophy is illustrated via narrative means.
Also note that the occasional appearance of a trope to avoid doesn't prevent the work from being Rational Fic, if it conforms to most of the other tropes.
