I²S
Inter-IC Sound — Philips' 1986 serial bus for moving digital audio between chips on the same board.
Three wires are enough: a bit clock (BCLK), a word clock (LRCLK or WS) that toggles between left and right channel, and a data line carrying the samples, most significant bit first. A master clock (MCLK) is often added as a reference for the DAC. Because clock and data travel on separate wires, jitter stays lower than in formats where the clock has to be recovered from the signal, such as S/PDIF.
Despite the name, I²S has almost nothing in common with I²C beyond the manufacturer and the superscript — there are no addresses and no shared bus. It sits between practically every SoC and its ADC in phones, sound cards and smart speakers, which is why a Raspberry Pi sound card can be sold as a little board that plugs onto the GPIO header.