A smiling yellow face with glasses, often with teeth showing, originally buck teeth on most platforms.
While this emoji is often used by people calling themselves nerds in a self-deprecating way, the nerdy glasses paired with buck teeth can, and often does, evoke anti-Asian stereotypes. The fact that the default color of emoji faces is yellow further pushes this emoji into racist "yellowface" territory.
Some platforms have redesigned nerd face over time to not have buck teeth, perhaps in acknowledgement of the harm this imagery may cause. Google, Facebook, and JoyPixels originally featured designs with buck teeth but have since changed (or completely removed) the teeth on nerd face.
Apple, Twitter, Microsoft, Samsung, WhatsApp, and other platforms still use designs for this emoji that include buck teeth.
📅 Nerd Face was approved as part of Unicode 8.0 in 2015
and added to Emoji 1.0 in 2015.