Cosa significa "Fi" in Wi-Fi?

I just got into a heated discussion about Wi-Fi. What does the “Fi” in Wi-Fi mean? I would have thought it potentially stood for “frequency interface” since all network adapters are classified as interfaces. However, I am not certain about this.

Preface

There has been a lot of discussion in the comments and other answers here about how to interpret the term Wi-Fi, of what it should or does mean by virtue of historical and common usage, and implied meaning. There is no right answer to that. This answer can only address what the term is officially supposed to mean and the historical background that has given rise to these arguments.

Wi-Fi Did not Originate as an Abbreviation

The Wi-Fi name and logo were simply designed as a trademark. To quote the article Wi-Fi Definition is Not Wireless Fidelity on Webopedia:

Background

Source: Wi-Fi [Wikipedia]

If you look at the brand names Interbrand has created, most are meaningless sounds that are catchy to say, or nonsensical combinations of word pieces used to create a new word. The objective of a brand name is to conjure an association in the user’s mind; the definition is the product. Interbrand’s proposal of Wi-Fi was likely because it had a letter pattern reminiscent of Hi-Fi and rhymed with it, thus making it a good marketing word.

As I will describe shortly, the Alliance was trying to promote the use of wireless LANs to the home market to transfer audio and video. The similarity to Hi-Fi was a good fit, but not because Hi-Fi meant High Fidelity.

Most people know that Hi-Fi had been shortened from High Fidelity. However, Wi-Fi was coined half a century later and Hi-Fi had evolved. It was no longer short for, or synonymous with, High Fidelity. Its last common usage was as slang for ubiquitous, consumer-grade audio equipment or reproduction.

So the link between Wi-Fi and Hi-Fi at that point was simply an association with music and multi-media, not the meaning of the syllables. Just because Hi-Fi was shortened from High Fidelity does not mean the “Fi” in every word that imitates the letter pattern stands for Fidelity.

Origin of Wireless Fidelity

After adopting the name and logo, some of the Alliance members had a problem with the concept that something that looked like an abbreviation did not have a literal explanation. As a compromise, it was agreed to include the tag line “The Standard for Wireless Fidelity” along with the name. This implied a word association without there actually being one. As Phil Belanger describes it:

Excerpt From: Wi-Fi isn’t Short for “Wireless Fidelity” [BoingBoing]

Further explanation from Belanger:

Excerpt From: “Wireless Fidelity” Debunked [Wi-Fi Planet via Web.Archive.org]

Conclusion

Officially, Wi-Fi has no meaning. The Wi-Fi Alliance created the impression that it stands for Wireless Fidelity and has spent the last 16 years trying to correct that mistake. However, the word association is still well entrenched and still repeated.

Addendum

The next generation replacement for Wi-Fi may be a technology currently in development, based on data transmissions embedded in LED room lighting. As described in another SuperUser post, the developer is among the people who believe Wi-Fi stands for Wireless Fidelity. As a cute knock-off of a cute knock-off, he coined the name Li-Fi, and explicitly called it Light Fidelity.

So regardless of the Wi-Fi Alliance’s original intent, Fidelity may be here to stay. The decision to use the tag line created the “gift that keeps on giving”.