An SLA (Service Level Agreement) is an agreed-upon time period within which a response and/or resolution should be provided for a ticket.
Within Freshdesk, you can create an SLA policy under Admin > Workflows > SLA policies > Add Policy. You can set the SLA Targets and set rules for which this SLA will have to apply.
You also have the option to associate specific Business Hours with the SLA so that the SLA applies only for that business hour (time period).