Probability is a numeric estimate of how likely an event is to happen. In cybersecurity, it helps defenders move from intuition to prioritization: instead of asking only whether a vulnerability is severe, teams can ask how likely it is to be exploited, detected, or blocked. That makes probability useful in scoring, forecasting, and risk triage.
In practice, probability appears in models such as EPSS, which estimates the chance that a public CVE will be exploited within a time window. A higher probability score does not mean an attack will definitely occur, but it can justify faster patching, tighter monitoring, or additional controls. In defense, probability is most valuable when combined with context like asset exposure, business importance, and existing protections.