A Postgres cluster is, roughly speaking, a server instance. That is, if you run two copies of postgres on the same box (One on the default 5432 port, another on

A Postgres cluster is, roughly speaking, a server instance. That is, if you run two copies of postgres on the same box (One on the default 5432 port, another on, say, 6543) and have each of those copies manage its own independent config, data, etc, then those instances are what Postgres calls a cluster.