Web parts are ASP.NET controls that can be added to web part zones. They are generally distributed as WSP files. Pre-2013, they could be developed off the hosting server. With 2013, WebParts for the most part have to be developed the hosting server for propery library inclusion.
I've been tasked with getting a dashboard going using Excel Web Access Web Parts. These weren't listed as an option, however, under the Business Data category. I accessed this menu through the ...