@TH3_INT3RN3T
(don't worry i am too) SORRY I'M GETTING BACK TO YOU SO LATE. But to answer your question, an apply fic is basically an original story or a fandom fan fic where you submit an Original Character (OC) through the forms of which an author provides. the requirements differ author to author but are usually the same, and from there your OC— along with the author's OC made for the fandom fic in this sense —is used to create a story where the author gets to portray your character in. Sometimes people ship oc/character or range from mysteries, even k-pop books, again, depends on the author and the heavy communication there usually is back and forth when figuring out characters. Some times an author might use a "slot" as a cetain application method, and all the slots get full, that's one way of telling the application for the apply fic is "closed". It helps though when the author makes it clear though. Please ask me if you have any more questions! :D