Template data is the standardized description of a template, used by the default VisualEditor, the optional 2017 wikitext editor and other tools to improve the template-editing experience for the user. Both VisualEditor and the 2017 wikitext editor include a wizard to edit templates, but for the wizard to be most useful, it needs to present specific information to the user about each template, such as a short description of the template's purpose and its parameters. This information is codified formally (by any wiki editor) using template data.
