A network is two or more devices connected so that they can exchange data. Your phone, a smart TV, a game console and the computers that hold your favourite website are all just machines sending messages to each other.

Networks come in sizes:

• A LAN (local area network) covers a small place such as a home, a school or an office. It usually hangs off one router or switch.
• A WAN (wide area network) joins networks across cities, countries and oceans.

Most conversations on a network have two roles. A client asks for something (your browser asking for a page) and a server answers (the machine that stores and sends the page). One device can play both roles: your laptop is a client when it browses and a server when it shares a file with a friend's laptop.