Surface Mount TVS Diode, Transient voltage surge suppressor, zener diode,

 ESDLIN1524BJ Series 18.9 V Bi-Directional Transil Diode ESD Protection - SOD-323

https://www.futureelectronics.com/p/electromechanical--circuit-protection--tvs-diodes/esdlin1524bj-stmicroelectronics-1009439