1.5 Access List Overview
1.5.8 How to use the wildcard host
A second common condition where Cisco IOS will permit an abbreviation term in the extended access list wildcard mask is when the administrator wants to match all the bits of an entire IP host address.

Consider a network administrator who wants to specify that a specific IP host address will be denied in an access list test. To indicate a host IP address, the administrator would enter the full address-for example, 172.30.16.29; then to indicate that the access list should check all the bits in the address, the corresponding wildcard mask bits for this address would be all zeros (that is, 0.0.0.0).

The administrator can use the abbreviation host to communicate this same test condition to Cisco IOS access list software. In the example, instead of typing 172.30.16.29 0.0.0.0, the administrator can use the word host in front of the address. An example of using this abbreviation as an access list test condition is the string host 172.30.16.29.