Reservations allow you to assign a dedicated number of slots to a workload. For example, you might not want a production workload to compete with test workloads for slots. You could create a reservation named prod and assign your production workloads to this reservation. For more information, see Reservations.

an amount of time that is allowed for a single event in a planned order of activities or events: I think I have a slot open in my diary. 1-hour/90 minute/4-hour, etc.