The Security Poverty Line is the point below which an organization can no longer be effectively secured with the resources it has. At that level, budget, staff, time, and tooling are too limited to maintain basic defenses consistently.
In cyber security, the term matters because security is an operational capacity problem, not just a product problem. If a team cannot reliably patch systems, manage identities, monitor alerts, and respond to incidents, then controls may exist only on paper. Attackers benefit from this gap by targeting the weakest, least maintained parts of an environment, while defenders use the concept to decide what must be simplified, automated, or prioritized. It is a practical warning that complexity, not just vulnerability, can create risk when an organization is asked to defend more than it can sustain.