Network address translation changes address information as traffic passes between networks. On many home IPv4 networks, a router lets devices with local addresses communicate through a public-facing address. Translation is part of the route, not a description of which person is using the connection.
A practical example
Two laptops on the same Wi-Fi may appear to a website through the same public IPv4 address. Each can still have its own local address. A public-IP lookup therefore does not necessarily distinguish individual devices behind that router.
What to check
If a game or application reports a NAT-related problem, copy the exact status and the task that fails. Establish whether ordinary browsing works and whether the device is behind a router or hotspot you control. Ask the network owner or service provider about the supported setup before changing inbound rules.
What it does not tell you
NAT is not a synonym for a VPN, encryption or anonymity. Do not enable broad port forwarding to fix an unexplained error. A problem involving incoming connections needs more specific diagnosis than a successful outbound website check provides.
Read the technical reference for the underlying definition. For a connection that is failing now, use the troubleshooting guide. To choose an app, follow the VPN selection worksheet.