Boost Your BIM, The Building Coder, and Punto Revit, there is sometimes a distinction made between macros and add-ins. So what's the difference? Harry Mattison provides the answer on his Boost Your BIM blog. Here's an excerpt...
"There are two different ways to work with the Revit API. In general, the code you write will be the same or almost the same in either case. Developing a macro is easier and simpler, but the trade-off is that you are limited in the development tools you use and how you share the macros with other people. Developing Add-Ins involves more set-up and some technical mumbo-jumbo to register the add-ins with Revit. A main upside of Add-Ins is that you are better able to distribute them to other people."
There's more information in this excellent post on Harry's blog.
Add-ins, macros, plug-ins -- we cover 'em all on the Revit Add-ons blog.