Adj. A person (usually female) who is not necessarily hot in the traditional sense of the word. This person may be considered somewhat universally attractive, but they have certain aspects of their personality, style of dress, and/or appearance that make them particularly appealing to nerds (i.e. a woman who likes comic books or roleplaying games, wears glasses and t-shirts depicting nerd subject matter, plays characters in nerdy films and TV shows, and/or who may be outside more popular social circles, for example). Note that a person who is nerd-hot need not necessarily be a nerd themselves.
Dude, do you think Tina Fey and Felicia Day are hot?
Nah, they're nerd-hot.