What is wi-fi?

[snotneck]

Is it possible for me to buy a device which transmits music or programmes playing on my PC to my stereo?

If so, what's it called and where can I buy it?

Is this wi-fi?

[fo3nix]

wifi is just wirelessly transmitting stuff, generally the internet.

the sort of thing you want can be done with the Airport Express from Apple, though cheaper products that do the same thing may be available.

[jenky]

There are quite a few of these, one of the best is the squeezebox,
http://www.slimdevices.com/welcome1.html?gclid =CMr-y8nu4okCFTU7MAodMQ7pFg
if your pc is on, this will find the music on it and you can browse and play through your stereo.
(Also lets you use a psp as a remote control so you can view artwork etc should you wish. )
Obviously a wireless router helps but most of the devices like this can be wired ito the network.