What does CIDR stand for in networking?

CIDR stands for Classless Inter-Domain Routing. This is a method used in networking that allows for more efficient allocation of IP addresses compared to the older classful networking method. CIDR introduces a flexible way to specify IP addresses and their associated routing prefix, which facilitates better utilization of the limited IPv4 address space and helps to reduce the size of routing tables.

By using CIDR, network administrators can group IP addresses into variable-length blocks, rather than the fixed blocks that classful addressing imposed. This leads to a more scalable and manageable routing environment, where IP addresses can be allocated based on actual need rather than adhering to rigid class boundaries.

In contrast, the other choices suggest alternative definitions that do not accurately capture the meaning of CIDR in a networking context. Each of these options introduces terms or concepts that are either invented or pertain to different aspects of networking, but they do not align with the established definition of CIDR as it is recognized in the field.