Refresh POP accounts is the latest Gmail Labs feature
Google developers have added a new feature to Gmail through Gmail Labs.
Refresh POP accounts is aimed at users who are importing emails from their other accounts through POP on Gmail.
Gmail automatically checks for new mails on third party accounts but this feature would let you manually refresh and get the latest mails.
Google developer Emmanuel Pellereau spoke about this feature addition:
Turn on “Refresh POP accounts” from the Labs tab under Settings, and the refresh link at the top of your inbox will not only update your inbox with your new Gmail messages, it will also fetch messages from any other accounts which you have set up.