We have :
Class A ,Class B, Class C ,Class D ,Class E in classful addressing of networks.
Class A :
Start Address:127.0.0.0 (which is wire address)
End Address :127.255.255.255
Hence you can use the next number that is : 127.0.0.1 to ping your local system.
There is no clear definition or answer for the same.Also you can have more reference at :