A letter in which an examining attorney sets forth specific requirements that the applicant must meet before an application can be approved for publication. An examining attorney will issue a priority action after consulting with an applicant or the applicant's attorney. Unlike an examiner's amendment, the priority action does not confirm resolution of the issues; instead, it explains the requirements still outstanding.
The applicant must respond to a priority action within 6 months from the date the priority action is mailed. If the applicant fails to do so, the application will be abandoned. Please note that examining attorneys have no discretion to extend the time for filing a response to an Office action.
The benefit of a priority action is that, if the applicant responds within 2 months, the application will be given priority in processing the response.
Source: U.S. Patent and Trademark Office.