What is Interdependence in MMOs?

It seems like anywhere you turn these days, you’ll find the creators of some up and coming MMO extolling the virtues of player interdependence in MMOs and how it’s making a comeback in their game. Titles like Crowfall, Saga of Lucimia, and Pantheon: Rise of the Fallen are touting the concept as something of a core design principle, promising that with it as a development objective, their game will usher in a return to the golden age of MMORPG communities.