Oh Trav-ee.

What you got against True Value Morpheus?

Think of instances (lemmy.world, kbin.social, sh.itjust.works, etc.) like planets. Each planet contains cities (or subreddits communities). Most of these planets are federated meaning that if you were born on one planet (have a login) then you can travel and participate the galaxy of cities and planets. If a planet defederates, then you can no longer travel there if you were not from there.