Science Fiction is often set in a world not our own. This could be an actually alien world, Earth of a different time, or just the world we know with a secret magical subculture revealed. To get the differences across, characters will, in casual conversation, tell us about the world in which they live. It's as if you were driving somewhere with a friend, and suddenly said "Gee, travel sure got a lot easier since we started basing our cars on the internal combustion engine!" or "As You Know, a red light means 'stop', while a green light means 'go'."
It's not simply limited to technology: Science Fiction writers want to explain everything. How does their evil plan work? What's their motivation for carrying it out? How old is the character? What's his backstory? What's the political history of the region he's living in? A good writer in other genres will probably know all of these things, but only in Science Fiction will the writer feel the need to actually tell us all of it — it frequently seems as though the author is less concerned that the audience won't understand what's going on, and more concerned that they might not believe that he/she's really thought everything all the way through. Sadly, this often serves the opposite purpose, making the audience all the more painfully aware when the explanations don't quite add up. The Continuity Nod abounds too.
When a writer gets sufficiently desperate to explain a bit of science or continuity, one can be left with the impression that he's not doing it so much for our benefit, as to make sure we know he did his homework. While other writers use Exospeak when it's completely unnecessary as a joke, the Expospeak Gag.
Note that some series have tried to avoid Expospeak. What they pick up in the mainstream, they often lose on the fringes, as fans accuse the writers of sloppiness because they ''didn't'' explain everything. Reflecting this trend, a New Media format of Expospeak was used in GunBuster, where it was limited to omake segments on the tapes/laserdiscs/DVDs, and completely separate from the main show.
A predilection for Expospeak hasn't prevented Police Procedural shows such as CSI from leaping to the top of the ratings, or many novels on bestsellers lists (Dan Brown's books are laden with Expospeak about different subjects), lending credence to the oft-expressed idea that the reason speculative fiction only seems to be in decline as a genre is because its tropes have been adopted by the mainstream.
Expospeak is facilitated by:
- As You Know — Note, though, that not all instances of As You Know are Expospeak: when an As You Know is used to reveal something that previously happened off-screen or to reference a previous episode, that's not Expospeak. When it's used to frame an explanation about how the world of the series works, it is.
- Techno Babble
- Mr. Exposition
- The Watson