N-days cause most real-world compromises because the patch is public, attackers can study it to build an exploit, and many systems are updated late. WannaCry (2017) and Log4Shell (2021) are well-known examples. Fast patching is the main defense.
A vulnerability that has already been disclosed or patched, n days ago, but is still exploitable on systems that have not updated.
N-days cause most real-world compromises because the patch is public, attackers can study it to build an exploit, and many systems are updated late. WannaCry (2017) and Log4Shell (2021) are well-known examples. Fast patching is the main defense.