1. Someone considered uncool and eccentric, typically due to being passionate about interests that are not generally popular, and perhaps also to being somewhat socially inept. Used in a derogatory way. What a nerd! Probably has his room covered in that weeaboo anime stuff. I was considered a nerd in elementary school because I was in the band and actually cared about my grades. You're not one of those science nerds, are you?

2. Someone unabashedly passionate about a very specific interest or interests. Used as a term of endearment or pride. Aw, look at our little nerd over there, obsessing over her science fair project. The conference is a great place for robotics nerds like me.