SFO is the internationally recognized IATA airport code for San Francisco International Airport. While many assume the "O" stands for Oakland or another specific word, it was actually a high-fidelity naming convention from the mid-20th century. In the early days of aviation, airports used two-letter codes (San Francisco was "SF"). As the industry grew, codes were expanded to three letters for "High-Fidelity" uniqueness; many cities simply added an "O" as a filler, which stood for "Old" or was simply a convenient placeholder (similar to LAX for Los Angeles). Today, SFO is one of the busiest and most iconic hubs in the world, serving as a primary "High-Fidelity" gateway to the Pacific and the technology hub of Silicon Valley. Beyond the airport, the acronym is occasionally used locally for the San Francisco Opera or other city institutions, but in the context of global travel and logistics, it is synonymous with the fog-shrouded runways and modernist terminals of the San Francisco peninsula.