User's Guide Prev Chapter 3. The cidr type holds a CIDR network. The inet type is designed to hold, in one field, all of the information about a host including the CIDR-style subnet that it is in. Note that if you want to store proper CIDR networks, you should use the cidr type. The inet type is similar to the cidr type except that the bits in the host part can be non-zero.
Functions exist to extract the various elements of the field.
This allows the type to be used as a straight host type by just leaving off the bits part.