Service Level
One or more metrics that define expected or achieved service quality.
Impact
Service levels provide the quantifiable target for operations.
Weinto take
Service Levels must be User-Centric. Don't measure "Server Uptime"; measure "Successful User Logins." The server can be up while the database is down, meaning the user can't login. From an infrastructure perspective, you are up; from a service level perspective, you are down.