What does net mean for an internet address?
When people refer to internet address they mean IP address. This
is an address composed of 4 sections separated by periods. There is
a associated network mask. The Network mask tells you which of the
bits of the IP address refer to the Network, and so which bits
refer to the device.
Example 192.168.100.0 with a mask of 255.255.255.0 means that
only the 4th part is the device address whereas 192.168.100 is the
network. This is a class C address which can have 254 devices.
It follows that if you don't know the network mask you can't say
which part of the IP address is the network!