Definitions of a Nerd:

A person who is single-minded or accomplished in scientific pursuits but is felt to be socially inept (by non nerds.)

Perjorative applied to anyone with an above-average IQ and few gifts at small talk and ordinary social rituals.

Term of praise applied to someone who knows what's really important and interesting and doesn't care to be distracted by trivial chatter and silly status games.

The word nerd and a nerd, undefined but illustrated, first appeared in 1950 in Dr. Seuss's If I Ran the Zoo. "And then, just to show them, I'll sail to Ka-Troo and bring back an It-Kutch a Preep and a Proo a Nerkle a Nerd and a Seersucker, too!"