Zero day is almost always used in the context of “the bug was unknown and first seen during an attacks”.
The alternative definition (that zero day means purely day of publicizing) would mean that if you had two bugs in a product and you notified the vendor of one. Then three months later published both, they would both be zero days, and should be treated as such.
A 0day means publicizing a bug without the vendor themselves having the potential to have a fix.
Very simply: if a virus comes out attacking a known but unfixed bug in MS software no one would call it a zero day. Every article would say it was a bug that Microsoft knew about but hadn’t fixed.
The alternative definition (that zero day means purely day of publicizing) would mean that if you had two bugs in a product and you notified the vendor of one. Then three months later published both, they would both be zero days, and should be treated as such.
A 0day means publicizing a bug without the vendor themselves having the potential to have a fix.
Very simply: if a virus comes out attacking a known but unfixed bug in MS software no one would call it a zero day. Every article would say it was a bug that Microsoft knew about but hadn’t fixed.