Port Address Translation (PAT) is a technique used in networking to allow multiple devices on a local network to share a single public IP address. It works by assigning different port numbers to each device's outgoing traffic, enabling the router to distinguish between them. This way, multiple devices can communicate with the internet simultaneously without needing individual public IP addresses. When a device sends data to the internet, the router modifies the source IP address to its own public IP and appends a unique port number. When the response returns, the router uses the port number to route the data back to the correct device on the local network. This method conserves IP addresses and enhances security.