The Address plus Port (A+P) Approach to the IPv4 Address Shortage is a technique for sharing single IPv4 addresses among several users without using stateful NAT. The technique is described in experimental RFC 6346.
Normal routing only uses IPv4 address to identifying which host traffic is destined for, A+P also uses destination TCP or UDP port. Each host is assigned a range of ports for which they receive traffic for, this also means they can only use these ports as source port when sending traffic.
A+P is similar but not identical to stateful NAT, as the A+P gateway does not need to keep track of every TCP or UDP flow.
RFC 6346