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]

But y'know what's cooler?

Log your system to a blockchain, while looking for 0days (which is
legal and helps national security), and catch your governments trying
to illegally stop you using their own!