The overload keyword, when specified with the ip nat inside command, translates multiple devices in the internal network to a single address in the IP address pool.

In this example, the NAT pool named "test" only has a range of one address. Another variation of this command is as follows:
ip nat inside source list 3 interface serial 0 overload
This command configures NAT to overload on the address assigned to the serial 0 interface.

When this variation is used, the command uses a list named 3 to determine the addresses in the pool With static NAT, translation mappings are created statically and are placed in the translation tables regardless of whether there is traffic flowing.

With dynamic NAT, the translation mappings table is populated as the required traffic flows through NAT-enabled devices.

Override is not a valid NAT option. There is no such option.