To what does "zero day" refer?

Question

Does "zero-day" or "0-day" (in context of software vulnerabilities and exploits) refer to the software release, or a particular type of exploit?

[I did not find an answer to this on SO. Though it is answered elsewhere on the Internet, my understanding of SO is that it's okay to ask/answer basic questions]

Answer 1

Wikipedia has two entries which are relevant:

• Zero-day virus
• Zero day attack

Answer 2

See http://en.wikipedia.org/wiki/Zero_day_attack.

Answer 3

Simply put it means that it [the exploit] was released before the company was notified, and had the opportunity to fix it, because the company had 0-days of notification.

Answer 4

A zero-day vulnerability or attack means that an exploit has been found active in the "wild" without being announced or the developers notified.

Answer 5

A zero-day exploit or vulnerability is an exploit for a bug that is not known to the general public (i.e. no patch was released for it).

Answer 6

Three major uses of "Zero Day"

• http://en.wikipedia.org/wiki/Zero_day_virus
• http://en.wikipedia.org/wiki/Zero_day_attack
• And also "zero day" warez (pirated) software: software cracked and/or released to the public by some pirate on (or before!) the day said software was available for sale.

I personally was aware of the third sense before the other two.