Exploit
Code or a technique that takes advantage of a vulnerability to make a system do something unintended.
A vulnerability is the flaw; the exploit is the thing that uses it. The gap between disclosure and a working public exploit has narrowed sharply, and for internet-facing software it is now commonly measured in days.
Whether a public exploit exists is one of the most useful inputs into patching priority, often more useful than the severity score alone, because it separates theoretical risk from what is actively being used.
Where this comes up
Exploit sits inside our cybersecurity and threats work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.