An IP address (Internet Protocol address) is a numeric label assigned to every device on a network. It's what lets a server on the other side of the world know where to send the reply when you load a page — the digital equivalent of a return address on an envelope.
Why devices need one
The internet works by moving small packets of data between machines. Each packet needs a source and a destination, the same way a letter needs a "from" and a "to." Without an address, there'd be no way to route a reply back to you, or a request forward to the right server.
Not quite a street address
An IP address is closer to a phone number than a street address: it identifies an endpoint, but it can move. Most home connections are handed a dynamic address by their ISP that can change over time, unlike a fixed physical location. It also doesn't pinpoint you precisely — it maps to a general area, typically your ISP's regional infrastructure, not your front door.
Two address spaces
You'll encounter two formats. IPv4 addresses look like 203.0.113.42 — four numbers separated by dots. IPv6 addresses look like 2001:db8:85a3::8a2e:370:7334 — longer, and written in hexadecimal groups. IPv6 exists because IPv4's roughly 4.3 billion addresses ran out; see IPv4 vs IPv6 for the details.
Public vs private
The address this site shows you is your public IP — the one visible to the wider internet. Every device on your home network shares it when talking to the outside world, while internally each device also has a private IP your router assigns. Read more in public vs private IP.