Spoilers

From UnknowableWiki

Spoilers are either little snippets, summaries or descriptions that 'spoil' the plot of something. It usually reveals something that was not mentioned before.

Many Harry Potter fans have had their books spoiled on the Internet and reading something someone wrote who didn't put a spoiler warning.

The Unknowable Room and many other Harry Potter fan sites have already posted on the news that asks members to follow a certain no spoiler policy, seeing as we are close to the release of Deathly Hallows. In case some people have already read the book and want to discuss it with a group of people, they can post a Spoiler Warning and thus let the readers decide on their own if they want to continue reading and have the books spoilt, or if they decide to close the window. These warnings prevent people from accidentally reading the spoilers.