according to this answer on ServerFault (http://meta.serverfault.com/questions/1610/what-does-first-rollback-mean-for-the-cleanup-badge):
"The first time you rolled an edit back. Say someone asked a bad question, then someone else edited it, but missed the point of the question in the edit. (If you have enough rep, or if it was your question) you can undo the edit by rolling it back. You get a badge for this."
"Just for clarification, "rollback" means you go to the "edit" link, and then click "rollback" on a previous version".
Hope it helps!
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