The term Wi-Fi is often used by the public as a synonym for wireless LAN (WLAN). Wi-Fi is supported by most personal computer operating systems, many game consoles, laptops, smartphones, printers, and other peripherals.
Basically it is a way for any hardware device to send and receive information to the Internet without a physical wire attatched. It is another way to transmit information over the airwaves like a traditional television antenna or radio signal.