0-day

Adjective

zero-day (not comparable)

1. Of warez, released less than a day after the official product release.
   • Back then, having "zero day warez" (brand new cracked games that are not even one day old yet) on your BBS first was a big status symbol.2020, Oliver Markus Malloy, Bad Choices Make Good Stories
2. (computer security) Of a vulnerability, newly discovered, and therefore still not fixed and possibly exploited by hackers or other criminals.
   • Although it's had tons of publicity, the IE zero-day vulnerability is so far only a real threat to people running IE6 on Windows XP, and you have to wonder about the competence of the companies actually affected by it[.]2010 January 18, Jack Schofield, “The IE zero-day vulnerability, Google, and you”, in The Guardian, →ISSN
3. (computer security) Of an exploit or its threat or an attack, benefiting from a newly found and yet unpatched or unmitigated flaw in software or hardware; using a zero-day vulnerability.
   • If your software is popular and has a high demand, you will want to defend against the "zero-day" cracker.2003, John Viega, Matt Messier, Secure Programming Cookbook for C and C++
4. Used other than figuratively or idiomatically: see zero, day.
   • Average residues of 1.44 and 2.18 mg/kg chlortetracycline were seen in liver and kidney, respectively, at zero-day withdrawal.

See all 6 meanings of zero-day