IP address (short for Internet Protocol Address) is a unique network address of a node in a computer network built using the IP protocol. The Internet requires global uniqueness of the address, while working in a local network requires uniqueness of the address within the network. In the IPv4 protocol version, the IP address is 4 bytes long, and in the IPv6 protocol version, the IP address is 16 bytes long.

In version 4, the IP address is a 32-bit number. A convenient form of recording the IP address (IPv4) is a record in the form of four decimal numbers with a value from 0 to 255, separated by dots.

In version 6, the IP address (IPv6) is 128-bit. The separator inside the address is a colon (e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Leading zeros may be omitted in the record. Consecutive groups of zeros may be omitted, and a double colon is used instead (fe80:0:0:0:0:0:0:1 can be written as fe80::1). More than one such omission in the address is not allowed.

An IP address is called static (constant, unchangeable) if it is assigned by the user in the device settings, or if it is assigned automatically when the device is connected to the network and cannot be assigned to another device.

An IP address is called dynamic (non-constant, changeable) if it is assigned automatically when the device is connected to the network and is used for a limited period of time specified in the service that assigned the IP address (DHCP).

A single domain name can be converted to multiple IP addresses in turn (for load balancing).

At the same time, a single IP address can be used for thousands of domain names with different sites (then they are distinguished by their domain name when accessed), which causes problems when identifying sites by IP address for censorship purposes.

Also, a server with a single domain name can contain several different sites, and parts of a site can be accessible via different domain names (for example, to isolate cookies and scripts to protect against cross-site scripting attacks).