'Wi-Fi' is used to mean a wireless network which you can use to transmit photos or communicate with other computers. Nearly all laptops and notebooks these days come with built in 'WiFi', or wireless networking, but it's not yet common on cameras.
Nikon's CoolPix S52c (now discontinued) was able to send pictures to Nikon's My Picture Town website where they could be forwarded as emails to other people. Samsung's ST1000 (pictured above) goes further, though, with the ability to email pictures directly.
Some professional D-SLRs have Wi-Fi add-ons that enable photographers to send pictures back to their clients without leaving their location - though most will use laptops which will be able to achieve the same thing much more easily.
The main limitation at the moment is that devices like these need an 'open' wireless hotspot which doesn't require any authentication. Most hotels, restaurants and other public buildings have 'closed' networks which only become available on payment of a fee, and then require an authentication process which is simple enough on a computer but more problematic on a device like a camera which lacks a keyboard.
