Classless Inter-Domain Routing (CIDR) is an IP addressing method that improves efficiency by allowing flexible subnetting and aggregation of IP addresses. Unlike traditional class-based addressing, CIDR uses prefix notation (e.g., 192.168.1.0/24), where the number after the slash represents the bits used for the network portion. This allows for precise allocation of IP addresses, reducing wastage and optimizing routing by grouping multiple networks into a single route (supernetting). CIDR enhances scalability, minimizes routing table size, and is widely used in modern networking, including ISP allocations and routing protocols like BGP. Learn more: https://en.wikipedia.org/wiki/CIDR