Well... I guess the best way to call it is a time loop? While we're here, time passes for us, but not back home. That's what everyone says, at least. [Neither of them have been back home in order to see that, after all.]
And it also means that people can arrive here from different points in time, with everyone overlapping. And from different dimensions and realities, it seems. Most people here seem to be from some version of Earth, but it's either a past version of our own or another version entirely.