Carrier Grade NAT, (CGN, CGNAT, CG-NAT) is also known as Large Scale NAT (LSN). Like regular Network Address Translation (NAT), it shares an outside IP address among multiple inside local (private) IP addresses. This feature is utilized to alleviate the IPv4 address exhaustion.
The difference with the legacy NAT solutions is that CGN provides a standardized (RFC 6264, draft-ietf-behave-lsn-requirements-09) transparent translation scheme (through EIM, EIF, hairpinning), and the ability to limit the resource usage per connection. CGN provides IPv4 preservation, and is an integral part of IPv6 migration.