Host bits
Host bits are the portion of an IP address that identify a specific host in a subnet.
The subnet mask determines how much of the address is used for network bits and host bits. For example, an IP (v4) address of 192.168.0.64/26 has a 6-bit host portion, because 26 out of 32 bits are reserved for the network portion. (See the main subnet article for details on how that calculation works.)
Within the host bits field, two values are reserved. If the host bits section is all zeros, it is a network address, and refers to the notional "wire" that the subnet's hosts transmit on. If the host bits section is all ones, it is a broadcast address. A packet bearing this address will be sent to every host on the subnet. All addresses between these two extremes are available for individual hosts, such as routers or workstations.