This question was “hotly” debated on a mailing list. Jon Pugh offered the definitive answer: “I believe I [am] in a position to make a definitive statement on the plurality of the name osax since I helped Donald Olson make up the term. First off, they are all lowercase. In multiples, we call them osaxen. In polite company, i.e. documentation, we call them Scripting Additions…[osax stands] for Open Scripting Architecture eXtensions. We wanted to call them osex, but didn’t think the Apple laywers would let us get away with that…Also, osaxen are not limited to scripting. If you have AppleScript installed and ANY program sends an event or uses a coercion defined in an osax, it will get called. Their use is not limited to AppleScript. However, AppleScript must be present for them to get loaded and used.”