As far as I can tell "installation media" is the most commonly used term
(Eg: RedHat, SUSE, Microsoft, Apple). While it might not be the ideal
term, it's worth mentioning that idiosyncratic documentation may also
have a "risk" of this kind. My vote is for "installation media" because
I've never seen any of the proposed alternatives in print. It
definitely needs "installation" for precision, because there are many
types of media, and "media" is a generic and neutral term.
That's a good argument IMHO, not mentioned before.
And given that most people were fine with this term in the first run
(except of Ben), and there is no perfect choice in this case anyway,
I will move back to "installation media" and to Justins review from
https://lists.debian.org/debian-boot/2019/09/msg00082.html