A spoiler is a piece of information in an article that reveals major plot details or plot twists, and thus may "spoil" the experience for any reader who learns the details of the plot in the same way rather than the work itself. The Dangan Ronpa Wiki features a "spoiler warning" to alert readers about the spoilers present in an article.
On character articles, plot information is listed about the character (some others too, if their plot concerns the primary article's), according to the occurrence of events in his/her story line. A warning is provided for such spoilers in these article, and it is best to avoid these if you do not want to be spoiled about the character. Generally, sections of articles possess a warning, but it is also possible that some articles may spoil from the beginning.
On episode articles, plot information is listed according to the occurrence of events and might shock a reader with no prior knowledge of the series. Such article may or may not contain a spoiler warning, but these articles generally spoil the readers. Prior warning might not be provided in these articles, and hence, the best practice is to avoid random episode articles.
On game articles, plot information is listed according to the occurrence of events in the game itself. Such articles reveal much information about the game itself, and hence are considered to be spoiling. Such articles also possess answers to puzzles present in the game, and should be avoided by those willing to complete the game by themselves.
New information considered to be too "shocking" for readers in any article is also considered to be a spoiler. A warning must be provided for such information, and it is best to avoid these, as these might greatly spoil a reader.