While in the editor, these can be defined in the Project settings window. A project can be dependent on any number of other projects. To be able to edit existing content, you need to be able to load that content. they are talking about creating/publishing/downloading projects other people made in the editor. So, when people talk about 'modding', 'creating mods'. 'Project' is simply what we call a mod in the editor for ease of use. When publishing a project in the editor, it puts itself online for others to download and enable in their game. (New content is simply loaded and added to the other content.) This page explains how these edits to existing content are handled by the system. This pack of custom content is called a 'mod'. When talking about 'Modding', we refer to editing existing content as well as creating your own.
