Of Transient Voltage Suppression (TVS) Diode
This particular type of diode is designed specifically to protect sensitive electronic equipment from voltage transients induced by lightning and other transient voltage events.
TVS diodes are used for the protection of I/O Interfaces, VCC bus and other vulnerable circuits used in telecom, computer, industrial and consumer electronic applications.
Subheading HS: 8541.10.
Source: https://rulings.cbp.gov/index.asp, July 10, 2017 (N287782)