Add-in

An add-in is a small extra program that adds new features inside a program you already have, without changing the program itself. It's a bit like snapping a card wallet onto your phone case: you don't have to replace the phone to get a wallet feature, you just attach the case. Add-ins work the same way, layering new tools on top of a program's existing screen and controls, without altering how you use that program.

That's why an add-in can't run on its own. It only works while a specific host program is open and running inside it. For example, if you install an add-in for a design program that automatically converts scanned part data, a designer can use that feature right in the screen they already work in, without having to learn a whole new program.

The article explains that it "is offered as an add-in for Autodesk Fusion, so it can be used by adding a separate tool into an existing CAD workflow." A common misunderstanding here is thinking an add-in is a standalone new program, but in reality it can't run without the existing CAD program and instead behaves like an accessory feature built into it.

Think of a document, design, or spreadsheet program you use often. Search for that program's name together with the word 'add-in,' and see if there are extra features, like automatic translation, table cleanup, or data conversion, that you can use without ever leaving the program.