0-day

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.

Stupid ploy used by every site that claims to link to pirated software but only leads to 70 year old naked grandmas.

The first day in Polytopia, used to make your first plays

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.