What is Thyristor, Triac thyristor, Process control, Overvoltage protection

 Snubberless Series TO-220-3 1200 V 25 A Through Hole Triac

https://www.futureelectronics.com/p/electromechanical--circuit-protection--protection-thyristors/t2550-12g-stmicroelectronics-1046626