"WiFi" is an anacronym for Wireless Network connection. In other words, with a "wireless" network card in your computer, IF your computer is within the signal range of someone's wireless network, you may be able to connect to it and enjoy network speed internet access.
However it is no guarantee. It all depends on whether or not the network is open to the public or not.
Wirless networks have a general range of 1000 feet. So we're talking pretty close to "line of sight" range. But it beats being tethered to a cord. :C
Hope this helps.