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 proper library inclusion.
Web parts let authorized end users modify the content, appearance, and behavior of web pages directly from a browser.
Questions having the web-part regards design, development, configuration, implementation and use of web parts.