Zero Subnet and Broadcast Subnet.

Subnet Zero

If a network address is subnetted, the first subnet obtained after subnetting
the network address is called subnet zero.

Example:

172.16.0.0

255.255.224.0

172.16.31.255

172.16.0.1 to 172.16.31.254

The first subnet (subnet 172.16.0.0/19) is called subnet zero.

The All-Ones Subnet or Broadcast Subnet

When a network address is subnetted, the last subnet obtained is called
the all-ones subnet.

With reference to the example above, the last subnet obtained when
subnetting network 172.16.0.0 (subnet 172.16.224.0/19) is called the
all-ones subnet.

172.16.224.0

255.255.224.0

172.16.255.255

172.16.224.1 to 172.16.255.254

Source:http://www.cisco.com