From mediawiki.org
Hello. Thank you for your contributions to MediaWiki. When editing an page on MediaWiki.org, you will see a small field labeled "Edit summary" shown under the main edit box. It looks like this:
Summary (?):
Please be sure to provide a summary of every edit you make, even if you write only the briefest of summaries. The summaries are very helpful to people browsing an article's history.
Template documentation