I think it referres to information that is reaveled about an アニメ または a Character etc that other people watching the 表示する may not yet know. Some people don't want to know what happens, befor they get to see it for themselves, because it can Spoil the surprise. that is why it is called a Spoiler:)
A "spoiler" is information that may "spoil" a book, show, または movie for someone. For example if someone wrote "I can't believe _________ died at the end of ________!" That would be a spoiler.
Sometimes with such questions I wonder why someone don't 検索 in Google when he something don't know... I just tick and knows everything Google, don't bite! Are people are so lazy that they must ask for something other? I will understood if it were something difficult to find, but this? Other 質問 that are really hard to find the answer are ロスト in 質問 like this one...
