NAT (Network Address Translation) is a router function that converts your device's private, internal IP address into a public IP address for internet traffic, then converts responses back again.
Your home network uses private IP addresses (like 192.168.1.5) that only work inside your local network. When you browse the web, your router intercepts outgoing traffic and replaces your device's private address with the router's public address. The internet sees only the router; your device stays hidden. When data comes back, the router translates it again and sends it to the correct device.
This serves two purposes: it lets multiple devices share a single public IP address, and it acts as a basic firewall by hiding your devices from direct internet access. Without NAT, every device would need its own public IP address, which would be expensive and less secure.
Real-world example: You're on a family home network with five devices. All five can watch videos, send emails, and play games simultaneously, even though your internet service provider assigned your home only one public IP address. Your router's NAT feature makes this possible.
When buying: Modern routers handle NAT automatically, so you rarely need to think about it. However, if you're gaming online or running a server, you might need to adjust NAT settings (such as port forwarding) to let inbound traffic reach a specific device. Check your router's documentation if you plan to do this.
Understanding NAT helps explain why your devices don't appear directly on the internet and why you may occasionally need to configure port forwarding for certain applications.