buck teeth
When the two upper front teeth project forward to such a degree, that they are very prominent and obvious.
Commonly seen in mouse or rabbit girls.
Sometimes used in derogatory stereotypes, such as with the stereotypical nerd depiction like with the nerd emoji or the old western stereotypical depiction of Asians like in Danbooru post #5065506.
Examples
See also
This tag implicates teeth (learn more).