An application admin is a role that grants full access to an application and its tables, scripts, and other components1. An application admin can create, modify, and delete any element of the application, as well as publish and install it2. An application typically has an application admin role that is automatically created and assigned to the application creator3.
Reference = 1: Application administration - ServiceNow Docs 2: Application admin role - ServiceNow Docs 3: Application roles - ServiceNow Docs