This is the spoiler template. It allows the contributor to make some text collapsible to either hide it or shorten the length of the article. To find go to Insert ► Template ►Search: Spoiler and then click on it. To edit the template click on it then scroll all the way down and you will see a section labelled 1 and 2. 1 is for the header which will be shown to readers and 2 is for the hidden text which will be hidden unless the reader clicks on the show button. Check out the Wiki Tools other that will help you.