What a hub is
A hub is a library of articles you embed on a website, yours or a client's, with one line of script. Visitors get a gallery and article pages that live on the site's own domain; you manage the content here.
Articles are written once and placed in hubs. One article can sit in several hubs. Each hub has layouts (the gallery and the entry page), a site path, and one or more subscriptions: the embed keys that sites use.