Wireless Fidelity?

This morning, as the WiFi signal waxed and waned from her tablet, my wife asked me "What's the 'fi' in 'WiFi' mean."

I told her it really doesn't mean anything, but it was intended to be familiar, thanks to professional audio equipment known as "Hi-Fi" for High Fidelity that means the output is as close to the input as possible, but that "Wireless Fidelity" really didn't mean anything.