Priority is the importance or attention given to a ticket based on the SLA. By default, there are four types of priority: Low, Medium, High and Urgent. Tickets with low priority are the least important and do not need to be solved immediately, while urgent tickets should be dealt with as soon as possible.
Setting this up from scratch? The ticket handling workbook builds a priority grid from impact and urgency, then the flow from triage through On Hold to closed, and gives you a policy to hand the team.