Glossary
EPSS
The probability that a CVE will be exploited soon.
The Exploit Prediction Scoring System, published by FIRST, estimates the probability that a CVE will be exploited in the wild within the next 30 days. It is a number between 0 and 1, updated daily.
EPSS answers a different question from CVSS. CVSS asks how bad it would be, and EPSS asks how likely it is. Using both gives a better order of work than either alone.