A Triac with a Diac feeding its gate is used in mains light dimmers and speed controls for power tools. They use a pot and capacitor to make a phase-shifted delay to turn on the triac early or late in each half-cycle of the mains voltage. Each time the mains voltage passes through zero volts, the load current drops to less than the holding current and it turns off. The phase-shift/delay parts turn it on in the next mains half-cycle.
You can learn about them if you want to make a light dimmer but they aren't used with guitars nor with audio.