Beginning with iOS 9.1, the operating system's library cache file makes mention of "LiFiCapability" alongside other hardware and software capability declarations. The change was spotted by Twitter user Chase Fromm and independently confirmed by AppleInsider.
Li-Fi works in a way not entirely unlike a traditional infrared remote control. Data is transmitted by rapidly modulating a light source, and received with a light sensor before being reassembled into an electronic signal.
Unlike your television remote, Li-Fi uses visible light and the modulation happens in a manner imperceptible to the human eye: that means the same bulb that lights your hallway can act as a data access point. It's also much faster, with theoretical throughput capacity of up to 224 gigabits per second.