When editing an article on Wikipedia there is a small field labelled "Edit summary" under the main edit-box. It looks like this:

The text written here will appear on the Recent changes page, in the page revision history, on the diff page, and in the watchlists of users who are watching that article. See m:Help:Edit summary for full information on this feature.

When you leave the edit summary blank, some of your edits could be mistaken for vandalism and may be reverted, so please always briefly summarize your edits, especially when you are making subtle but important changes, like changing dates or numbers. Thank you. –