Spoiler is slang for any element of any summary or description of any piece of fiction that reveals any plot element which will give away the outcome of a dramatic episode within the work of fiction, or the conclusion of the entire work. Because enjoyment of fiction sometimes depends upon the dramatic tension and suspense which arises within it, the external revelation of such plot elements can "spoil" the enjoyment that some consumers of the narrative would otherwise have experienced.
As a tag, denotes that a picture shows a spoiling element to a show or comic which may ruin the story for some.
Out of consideration for fellow users of this site, please keep spoilerish information out of danbooru wiki pages, and mark any and all spoilers posted in comments or on the forum with spoiler tags.
Read the full article.