The is a common bidirectional trigger diode (DIAC) . It is typically used in phase control circuits (e.g., light dimmers, motor speed controllers) to trigger a TRIAC.
The DB2 is a silicon bi-directional trigger diode (DIAC) commonly used in power control circuits, such as light dimmers and motor speed controllers, to trigger triacs. Diac Db2 Datasheet Pdf 14