Private IP addresses are unique identifiers assigned to devices within a local network, such as a home or office. These addresses are not routable on the internet, meaning they cannot be accessed directly from outside the local network. Common ranges for private IP addresses include 192.168.0.0 to 192.168.255.255, 10.0.0.0 to 10.255.255.255, and 172.16.0.0 to 172.31.255.255. Devices using private IP addresses communicate with each other within the local network, while a router typically uses a public IP address to connect to the internet. This setup enhances security and conserves the limited number of available public IP addresses.