WhiteHouse.com ... A zero-day is a computer-software vulnerability either unknown to those who should be interested in its mitigation or known and without a patch to correct it. Until the vulnerability is mitigated, hackers can exploit it to adversely affect programs, data, additional computers or a network

[Undiscussed Horrific Abuse, One Victim of Many]

Here's the link unadorned: https://en.m.wikipedia.org/wiki/Zero-day_(computing)

0days were collected by security peeps for some time, until too many
of them were arrested for things others used their systems as proxies
to do, and now governments and hacking businesses have so many 0days
that we're turning into a planet of techno-oppression.

Recently, people decided they liked being unilaterally surveilled by
their governments! Never before in the history of our species, has
that been expressed. I suspect it isn't true.