I changed the core software being used to build this website to  Drupal - which variously defines itself as a "platform" and a "system" for "content management."  In 30 words, Drupal defines itself in a single paragraph, with two-sentences, at the entry into www.drupal.org, as a “platform”:

Drupal is an open source content management platform powering millions of websites and applications. It’s built, used, and supported by an active and diverse community of people around the world.