An SLA defines the agreement between the service provider (your organization) and end user (your customer) in terms of aspects of the service provided, such as its scope, quality, or turnaround time.
In the context of support service, an SLA will define different response times for different types of support requests. For example, severity 1 requests will have a response time of one hour, and severity 2 requests will have a response time of four hours.
Jira Service Desk lets you define SLA requirements based on response time. You can set up the rules on how response time will be measured, and the goals for each rule.
