Allocation
It includes assigned IP addresses, reserved IP addresses, and excluded IP addresses.
Lease
It means that the IP addresses are assigned and still in use.
Available
It is the status of IP addresses that can be assigned to any client.
Availability
The ratio of the total number of IP addresses in all DHCP pools minus the assigned.
Expire
if a DHCP client does not "renew" its IP address within the lease time, the DHCP server sets the address to "expired" and the server can lease the address to other hosts.
Release
The client may issue a message to release the address back to the server when the client no longer needs the address[1].
The server can lease the address to other hosts.
Decline
DHCP Client sends the DECLINE messages indicating network address is already in use to the server.
The server sets the address as "decline" and does not lease it but leases another IP address to the client.
The server changes the declined address's state to "available" after 20 minutes.
Renew
A DHCP client may renew to extend its lease prior to half of the lease time and can keep network connections.