By its IP address
It's called an IP address. Every device (PC, Tablet, etc.) that is connected to the Internet has one.
destination host address
An IP Address, or Internet Protocol Address. Each device has one.
Because they need a device to communicate with a distant network through. These devices are called gateways, and are normally routers. The hosts on a segment need to have knowledge of the gateway device in order to communicate outside the segment. In most environments, the local network will have an internal addressing scheme, one that is not routable on the internet, so there needs to be a device that can translate the internal addresses (non routable on the internet) into external addresses (routable on the internet). Of course this device needs to be connected to both the internal network and the external network to be able to send traffic between them.
Host
In a Local hosts file.
A host on a network is generally a device with a unique mac address (hardware address, set at the factory) It can be a PC with a network device, a network switch, a printer etc etc hosts can have an IP address mapped to their mac address's
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing.
The network part of an IP address indicates the network to which the host belongs. The host bits or host part of an IP address points to the actual device that has an IP address on the network. It can be a computer, printer, router or any device with an IP address that has the same network part.
172.16.15.20
The default gateway is the first IP address of the device that a client computer will look for when attempting to gain access outside the local network. This device could be a router, server, or other similar device; it is the device that grants access to the internet or other networks.
That is called an IP address, and is made up usually based off of location, and your internet service provider (ISP)IP address is the logical address which serves as Identity for the Host device on a Network.