NAT (Network Address Translation) is the modification of an IP address using IP packet headers via a routing device, providing the ability to map an IP address inside of a network to a different IP address outside of that network.

A DNAT (Destination NAT) is a NAT defined specifically for changing the destination IP address of inbound packets.

A SNAT (Source NAT) is a NAT defined specifically for changing the source IP address of outbound packets.