This tool shows the common pages that two or more editors have both edited, sorted by minimum time between edits by the users. In other words, if the editors made an edit to the same page within a short time, that page will show up towards the top of the table. In general, when two users edit a page within a short time, chances are high that they have interacted directly with one another on that page.
Click on the "timeline" link to see the edits that both users have made to the page in chronological order.