"Spoiler templates" are templates to help inserting content into pages that remains invisible at first, except for some sort of toggle switch and placeholder, and appear only after the reader flipped the switch. Note, however, that such functionality is (and probably has to be) based on JavaScript code effecting the change in the browser; A reader who has JS disabled or blocked or uses a JS-unaware browser will likely see the spoilers right away.

Small spoilers that do not contain wikitables can be created with the Spoiler template. For spoilers with wikitables (but still having a box around them), see the SpoilerBegin template. To make normal text - like entire paragraphs - be hidden after the page loaded, use the HiddenText template, and the HiddenWords template to insert a very short spoiler line-break-lessly into a paragraph.

Also note that Wikia has a help page on "collapsing" a page's HTML elements (without the use of the intervening templates layer).