An availability target is the stated uptime level a service aims to maintain, usually expressed as a percentage such as 99.99%. It tells customers how often the system should be reachable over a given period, but it is a service objective, not a guarantee that outages cannot happen.
In cyber security, availability targets matter because attackers often try to disrupt access rather than steal data, for example through denial-of-service traffic, ransomware, or account compromise that breaks administration. Defenders use the target to plan resilience: redundancy, monitoring, backups, rate limiting, and incident response all help keep services near the promised level. A high target is useful, but it only works when the underlying access control and operational practices are strong.