An SLO, or service level objective, is a measurable target for how well a service should perform from the user’s point of view. Common examples include 99.9% login availability, a checkout latency target, or a maximum error rate for an API.
SLOs matter in cyber security because attacks often show up first as user-impacting failures, not obvious server alarms. A DDoS flood, credential-stuffing campaign, or ransomware disruption can push a service past its latency or availability target even if some infrastructure metrics still look normal. Defenders use SLOs to measure real impact, prioritize incident response, and decide when to preserve an “error budget” by slowing risky changes or adding protections to critical paths.