pg_isready
DatabasesPackage: postgresql-client
Says whether a PostgreSQL server accepts connections, through an exit status. The readiness test of a deployment script or a healthcheck, with no password and no query.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
pg_isready -U- The role used to test that the server is accepting connections.
Lessons that teach it
No lesson names it among its useful commands; it appears inside other lessons' command lines.