This Integer32 object identifies which NAT pool is applied when Network Address Translation is performed on packets that match the associated access list entry. It matters to an administrator because it is the link between an address range (defined by the Start/EndAddress pair) and the specific pool of translated addresses those packets get mapped into. For example, setting this to pool ID 3 would direct all traffic matching that access list entry to be translated using whichever public address block is configured as NAT pool 3.