This is the template used to put a banner at the top of an article to identify it as outdated, i.e. an author signals that he thinks that an article needs to be updated to reflect recent changes.
You can get this banner by inserting the following template in your article (usually at the beginning):
If only a section should be marked incomplete, use following at the beginning of the section:
This will also insert your article in the Category:Articles in need of updating.