Original: Most often today , NAT is used in conjunction with network masquerading ( or IP masquerading ) which is a technique that hides an entire address space , usually consisting of private network addresses ( RFC 1918 ) , behind a single IP address in another , often public address space .
Simplified: Masquerading is the mechanism that hides an entire address space , usually consisting of private network addresses ( RFC 1918 ) , behind a single IP address usually in the public domain address space .