NAT is a method used to modify IP addresses in packets while they are in transit across a router or firewall. The main goal of NAT is to map private IP addresses to a public IP address, enabling devices in a private network to access the internet through a single public IP.
Masquerade
Masquerading is a special case of Source Network Address Translation (SNAT) and allows you to masquerade an internal network (typically, your LAN with private address space) behind a single, official IP address on a network interface. SNAT is more generic as it allows to map multiple source addresses to several destination addresses.
Definition of masquerading (verb)
pretend to be someone one is not. “a journalist masquerading as a man in distress”