Terminology gaps around WAL

I sometimes struggle to come up with the right term for the following
concepts, which come up a lot:

* The abstract set of WAL records that all originate from a single
initdb and share a system identifier; including all timelines, and
including old records that may have been deleted a long time ago.

* The "stuff" around that specific set of WAL records, such as running
instances, warm standbys, PITR'd instances, inactive instances, base
backups, and WAL archives.

"Database cluster" doesn't fit either of these. The docs define it as
"a collection of databases that is managed by a single instance of a
running database server." [1]

Do others already have good terms for these concepts? Is it worth
trying to invent and document some?

Regards,
Jeff Davis

[1] https://www.postgresql.org/docs/current/creating-cluster.html