The story
Coined in analogy to Hi-Fi as a trade name developed for the Wireless Ethernet Compatibility Alliance (later Wi-Fi Alliance). Often analyzed as a shortened form of wireless fidelity (similar to how hi-fi is short for high fidelity); this is possibly due to the former slogan of the aforementioned Wi-Fi Alliance, The Standard for Wireless Fidelity.
Etymology from Wiktionary, CC BY-SA 4.0.