SLA for Incident Managemenent is about measuring time with timers to check that processes are executed in due time.

Service Level Agreement Management is directly implemented in the itil-common bundle with a few entities and are using Business calendars to measure time with hollidays time zones and business hours.

Service Level Agreement Definition

The SLA template (or definition) is the itilServiceLevelAgreement entity.

You can have the list of SLA with the menu IncidentManagement / SLA