What does it mean to be a fan on hiatus? To someone who is not familiar with the catchphrase, it may seem to mean that a fan would take a certain length of a break from being an active fan of 'this' show or 'that' movie. It sounds like a vacation or holiday taken to help deal with the hard work it takes to be a fan.
It doesn’t mean that at all.
To be a fan on hiatus sucks because you have no choice in the matter. It's when there is a break between or during a television series or set of movies. The story being told is put on pause, usually with a fantastic cliff hanger that leaves questions unanswered and theories abounding.
A fan has no control over a how long a hiatus will last. Many times a show or series will have a set amount of time put aside for a break and a set date for when the show will return. Other shows, such as BBC Sherlock, know no such luxury. The fans of Sherlock waited a year between season one and season two, and they waited two years between the second and third season. They are on hiatus now for who knows how long.
So what does waiting like that do to a fan?
The effects vary from fandom to fandom. Some fandoms remain sane to a certain extent; others are known for their psychotic methods of dealing with a sudden halt in their stories. (It should be said that no fandom is ever and could never be in their right mind.) Each collective group of fans has their own level of insanity, some being more or less insane than others. The level of insanity can be deduced from the fanfiction, fan-art and mad guesses at the next episode that the fandom produces during a hiatus. The longer the hiatus, the more ridiculous and crazy a fandom will grow.
This situation could be seen as a bad thing for anyone who can be counted on the outside of a certain fandom. It is, in fact, one of the things that brings similar fans closer together. A fandom does not wither away during a break, it grows stronger and crazier until it is a force to be reckoned with.