Divisional Application

A patent application that is filed as a "child" of an existing "parent" patent application. 

A divisional application can usually be filed at any point while the "parent" patent application is pending (i.e. before it is either granted or refused) - however, there are significant variations in the rules between jurisdictions. 

A divisional (or child) application can be used to pursue protection for a different set of claims from those of its parent application.  The divisional application benefits from the same filing (and priority) date as the parent application.  However, the claims of the divisional application can only relate to subject-matter that has been disclosed in the parent application (whether in the description or the claims as originally filed). 

Divisional applications are commonly used in response to unity objections being raised against the claims of the parent application.  They can also form a component of more advanced patent strategies.