An exclusion range would be the reservation of IP Addresses the DHCP server does not assign out. These addresses, the network ADMIN would assign.

(Taken from a Dell Website) DHCP reservations and exclusions are both intended to allow machines in a DHCP environment to maintain consistent addresses, but from the DHCP server's perspective, there are significant differences between the two:

A reservation maps a media access control (MAC) address to an IP address. MAC addresses are typically hard-coded into network adapters, so that anytime a machine with a reserved MAC address requests a lease from the DHCP server, it will always obtain the same IP address. A reservation should be used if a machine needs to obtain its address from DHCP, but this address must not change. An exclusion removes an IP address or range of IP addresses from the pool of addresses that are given out by the DHCP server. The server will not give out excluded addresses. Therefore, a reservation should be used if a machine has a static IP address that falls within the DHCP address pool. This will prevent another machine from leasing the same IP address.