This semiconductor device (diode) has two terminals allowing current to flow in one (forward) direction only. Silicon diodes are the most common semiconductor PN Junction diodes which are formed from materials such as selenium, and germanium used predominantly in LED's whose characteristics are identical to "normal" diodes.
Useful sources of information:
https://www.britannica.com/technology/diode
https://www.electrical4u.com/diode-working-principle-and-types-of-diode/
https://www.lifewire.com/applications-of-diodes-818815
https://www.learnabout-electronics.org/Semiconductors/diodes_20.php
https://components101.com/articles/introduction-to-different-types-of-diodes
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