An IP address (Internet Protocol address) is a unique number assigned to every device connected to the internet. Just as a phone number lets people reach you by phone, an IP address lets other computers find and communicate with your device on the internet.
There are two versions of IP addresses in use today. IPv4 uses a format like 192.168.1.1 - four numbers separated by dots, each ranging from 0 to 255. This system can create about 4.3 billion unique addresses, which seemed like plenty when it was designed in the 1980s. However, the explosion of smartphones, computers, and IoT devices has exhausted the available IPv4 addresses. IPv6 was created to solve this shortage, using a longer format like 2001:0db8:85a3::8a2e:0370:7334 that can generate a virtually unlimited number of addresses.
IP addresses are divided into two categories. A global (public) IP address is unique across the entire internet and identifies your network to the outside world. A private IP address is used only within a local network, such as your home Wi-Fi. When multiple devices connect to your home router, they each get a private IP address internally, but they all share a single global IP address when communicating with the internet. The router handles the translation between private and public addresses using a technique called NAT (Network Address Translation).
URL shortening services record the IP addresses of users who click on links. This data powers geographic analytics - since IP addresses can be mapped to approximate locations at the country or city level, services can report where clicks are coming from. However, an IP address alone typically cannot identify a specific individual.
Most home internet connections use dynamic IP addresses, meaning your ISP assigns a different address each time you connect. Businesses and servers often use static (fixed) IP addresses that never change, which is necessary for hosting websites and services that need to be consistently reachable. You can find related books on Amazon.