ISU is the extension given to the files associated with the installation package management tool InstallShield. ISU is a file included with installation packages that allows you to properly uninstall the application from the system. It is a file in the form of an uninstall script.

ISU files allow for the thorough deletion of all data used by the installed application without the need to search and delete them manually. Additionally, some installation packages make entries in the system registry that should not be removed by the user.