CIDR notation, or Classless Inter-Domain Routing notation, is a method for representing IP addresses and their associated network prefixes. It combines the IP address with a suffix that indicates the number of bits used for the network part of the address. For example, in the address 192.168.1.0/24, the "/24" signifies that the first 24 bits are used for the network, while the remaining bits are available for host addresses. This notation allows for more efficient allocation of IP addresses compared to the older classful addressing system. CIDR helps reduce the size of routing tables and improves the flexibility of IP address assignments, making it easier to manage networks of varying sizes.