THREAT‑WATCH
Glossary
Zero-Day Vulnerability
A software flaw that's exploited by attackers before the vendor has released a fix, or is even aware of it.
'Zero-day' refers to the vendor having had zero days to fix the flaw before it was exploited or disclosed. Because no patch exists yet, defense relies on detection of anomalous behavior (rather than known-signature matching) and rapid patching once a fix ships, which is why continuous monitoring matters even for fully patched environments.