A program utility that enhances a primary program;
in RC-WinTrans, a software component that extends the application's functionality.

Technically, an RC-WinTrans Add-On is a VBA macros file (file extension = .macro) with at least one procedure implemented for execution.  The functionality is coded using Microsoft Visual Basic for Applications (VBA) and can do virtually anything a user (third-party manufacturer or needs it to do in order to extend RC-WinTrans' capabilities.