Spoiler

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A spoiler, named because they sometimes "spoil" a fan's enjoyment of the canon, is information (usually plot-related) about upcoming or recently-released serial source information. 
==History of the Term==
Possibly the first print use of the term was in the April 1971 issue of National Lampoon. In that magazine, Doug Kenney wrote an article called "Spoilers" that listed spoilers for famous films and movies. 	Remembering The Late Doug Kenney, ‘National Lampoon’ Cofounder And Possibly The Funniest Man Who Ever Lived by Stoogeypedia (December 10, 2021) 
Another early use was mentioned in September/October 1980 when a fan chided another for giving away the ending to a story and wrote: 
 
An example from May 23, 1981 by Bruce Hamilton: 
Another example is from June 8, 1982 by Wayne Hamilton: 
From 1985: 
A 1988 use: 
==Definition and Types==
What is or is not a spoiler is often a matter of debate. Creator statements, such as from interviews, are not generally considered to be spoilers unless they refer to material that will be explicitly featured in canon later on. 
Some fans also consider information about what actors will appear in what episodes of a tv series to be a spoiler; for instance, the surprise return of a long-lost character could be spoiled if fans know that the actor who plays that character is returning to the show. These are often referred to as "casting spoilers."
"Mood spoilers" are another type of spoilers. On Livejournal and other journalling sites, the author of a post can often specify what "mood" she is currently in, such as "elated" or "depressed." Some fans believe that even in the absence of all other spoilery information, indicating one's mood in this way can be spoilery. A mood spoiler can also be found in a title or an lj-cut; for instance, if a fan who was well-known to be a die-hard shipper of a certain pairing made a post titled "OMGSQUEE BEST EPISODE EVER," it could possibly be inferred that there had been positive developments regarding her OTP. Other fans have stated that it's not so much a single mood spoiler that is the problem, but that an entire flist full of various mood spoilers makes it somewhat impossible to not draw inferences about the quality of, or new developments in, new canon.
The term spoiler is sometimes used to refer to a fan who shares spoilers. This term describes their fannish activity and doesn't necessarily carry negative connotations. In some fandoms, spoiler communities (communities of fans seeking out spoilers) are common and trusted spoilers sometimes achieve BNF status within these communities. An associated term is foiler, which refers to fake spoilers or fans who intentionally share fake spoilers.
==Community Standards==
Many communities require spoiler warnings or outright ban spoilers in posts. Spoilery information (for discussion) generally has an expiration date, after which it is acceptable to discuss without warning other users. For example, an expiration date could be one week after the US or UK air date, for a television series, or one month after the release date of a comic book. Since fans in different geographical regions may not be able to view episodes for weeks, months, or even years after their original air dates, some fans and some fandoms have longer statutes of limitations. 
Fandoms that actively cultivate new fans, such as Farscape fandom, are often careful to welcome viewers watching the show for the first time without spoiling them for future plot points.
==Spoiler Protection==
It is common to give a spoiler warning in the header of a fan fiction story if it contains numerous references to a specific episode or book. This is far more common in the immediate aftermath of the episode, when many fans either may not have had a chance to view the new canon, or may be specifically seeking out fan fiction that deals with events in the new canon.
One common tactic for encoding spoilers, often used on Usenet newsgroups, was ROT13. 
An example of a 1994 "spoiler plate: 
By the time fandom had taken up residence on mailing lists, it was more common to use the word "Spoiler" in the subject line and to provide "spoiler space" -- multiple lines of space before the spoilers appeared. On blogs and Livejournal-type services, spoilers are more often put "below the cut", requiring a reader to deliberately click a link to see the spoiler.
 
Some fans also use HTML to hide spoilers; for instance, putting spoilers in white text on a white background. This requires the reader to highlight the text in order to be able to view the spoilers; however, it is not always implemented correctly, sometimes resulting in unintentional spoiling. Florahart, PSA regarding whiting out things you want someone to have to highlight to see., accessed June 07, 2009. In addition, this formatting may not be accessible to, or may not work to obscure the spoiler for, all readers, such as those who browse the internet using screen-readers.
A 2010 example of the tightrope some fandoms ask their fans walk is illustrated by this correction by a Live Journal Professionals community mod to a new fan who'd posted a fiction recommendation: 
==Controversy==
Some fans are more sensitive to spoilers than others. Some fans even self-identify as spoilerphobic, while others do not find that their enjoyment of canon is ruined by major or even mild spoilers. The relationship between spoilerphobic and non-spoilerphobic fans is sometimes fraught. 
Spoilerphobic fans often request that other fans take precautions to avoid posting spoilery information. Non-spoilerphobes may feel that they are being asked to go to unreasonable lengths in order to protect over-sensitive spoilerphobes. On the other hand, spoilerphobic fans may feel that their requests are entirely reasonable, and a refusal to comply is callous and rude.
The conflict between the spoilerphobic and spoiler-"philic" is parodied on the fandom_wank wiki in its spoiler template.
==The Spoiler and Warning/Label Debate==
In 2005, a fan pointed out what they felt to be a disconnect in expectations between fans who didn't want to be spoiled regarding canon details, such as an episode, movie, or book, and those who insisted upon labels and warnings for fanfic: 
==Spoiler Communities==
* Idealists Haven (X-Files)
* Spoiler Slayer (Buffyverse)
==Meta/Further Reading==
* Something Rotten on the Internet by Mary Jean Holmes (2002)
* by cereta (April 1, 2003)
* Spoiler Alerts Need To Die by Alex Mell-Taylor (May 3, 2019) 
* at The Daily Dot (2015)
==References==