Session is powered by a community-run network of decentralised nodes. These nodes act as the servers that help route messages from user to user.
Session also uses onion-routing, so instead of relying on just a single node, it routes your messages through 3 randomly selected nodes. This is what is referred to as your "path".
This path will remain the same as long as one or more of the paths do not fail 3 times and become unreachable. If they do, Session will attempt to reset your path with a new node. Once established, your connection will be restored and a new path will be set.