Which technology allows a large number of private IP addresses to be represented by a smaller number of public IP addresses?

Network Address Translation (NAT) is the technology designed to translate private IP addresses used within a local network to public IP addresses for communication over the internet, thereby conserving public IP address space. Specifically, NAT Overload (PAT) maps many private IPs to a single public IP using different port numbers.

NTP (Network Time Protocol) is used for synchronizing clocks over a computer network, not for IP address translation.

RFC 1631 is an informational RFC that describes the IP Network Address Translator (NAT) functionality, but NAT itself is the technology.

RFC 1918 defines the private IP address ranges (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), not the technology for translating them.