This tab in Gmail has been around for months now. It was reportedly added by Google in an effort to save people time, and reduce the amount of promotional, yet not-quite-spam, emails that we're all forced to see on a daily basis.
Last month Gmail introduced a new "Unsubscribe" link at the top of emails in your inbox. The purpose of this is to make it easier for people to unsubscribe from mailing lists they're on, without searching in the email footer for the link. The more easily people can unsubscribe, the less likely they are to click the "Spam" button, which hurts your sender score.