wi-fi

from The Free On-line Dictionary of Computing (8 July 2008)

wi-fi

   <networking> Either of two different incompatible radio-based
   {LAN} {protocols}, namely {802.11b} (which speaks {DSSS} at
   2.4GHz) and {802.11a} (which speaks {OFDM} at 5GHz).

   The term was invented by the marketing departments of wi-fi
   equipment manufacturers.  It is, notionally, short for
   "wireless fidelity", on the analogy of hi-fi for "high
   fidelity" audio.

   (2003-09-02)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

WIFI
       WIreless FIdelity [alliance] (WLAN), "Wi-Fi"

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

WIFI
       WIreless FIdelity [certificate] (WECA, WLAN), "WiFi"