Source : Free On-Line Dictionary of Computing

Classless Inter-Domain Routing
     
         (CIDR) /sid*r/ A scheme which allocates blocks of
        {Internet addresses} in a way that allows summarisation into a
        smaller number of {routing table} entries.
     
        A CIDR block is a block of {Internet addresses} assigned to an
        {Internet Service Provider} (ISP) by the {Internic}.
     
        CIDR was introduced to enable the use of more sophisticated
        {routing} protocols such as {OSPF}.
     
        See {RFC 1467}, {RFC 1518}, {RFC 1519} and {RFC 1520}.
     
        [Is this true?  Relation to classes?]
     
        (1997-03-06)