The Land of Aaa is a non-canonical name of questionable authenticity that has been used to describe the gender-swapped setting of the episodes "Fionna and Cake," "Bad Little Boy," and "The Prince Who Wanted Everything."
It appears in episode summaries distributed to television listing sites like TV Guide.
However, writer Adam Muto and lead character designer Andy Ristaino state that they have never used that name, and that it may have been made up by the marketing department. Adam Muto has also criticized TV Guide before. Natasha later stated that she despised the name and that it is completely made up.
In the actual episode, Ice King reveals that the tale takes place in Ooo, just like regular continuity. It is confirmed, however, in writing in the Adventure Time Encyclopedia that it takes place in the "Fan-Fictional Land of Ooh" as quoted by the Ice King, where he does not exist, clearing things up further by contrasting and saying that she (Fionna) does not exist in Ooo. Many fan-fictions made before and after the official airing of "Fionna and Cake" use the term Land of Aaa even though it is not canonically correct.
The Land of Aaa name was used in Winter Breakout on the Adventure Time Facebook Page.