1) warez obtained on the day of, or slightly before, its official (legal) release.
2) Information that is not publicly available until it is rapidly disseminated in the online community. Often contains the details of new computer vulnerabilities, allowing exploiters to comprimise computer networks before system administrators have a chance to secure their networks.
Dude, do you have access to any 0-day? I need to get my hands on the new version of Windows.
by Evan B March 14, 2005
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Stupid ploy used by every site that claims to link to pirated software but only leads to 70 year old naked grandmas.
The only 0 day warez linkz site on the net, period!
by Jeffery Kark July 8, 2003
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When an attention seeking emo/wemo tries to go so many days without cutting themself, then they fail. (They go back to day 0)

Whenever something bad happens, no matter how pointless, say 'Day 0' to mock the attention seekers, but also as a sign of respect to people who cut because of mental illnesses.
Luke: Damn I just stubbed my toe!
All: DAY 0!
Kristen: I forgot my homework!
All: Day 0!
Sam: I'm on Day 41! I hate that number!
All: Day 0
by Day0FTW April 17, 2012
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The first day in Polytopia, used to make your first plays
"That vengir made a swordsman on day 0"
by Billy Stamina April 15, 2021
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