WordNet (r) 3.0 (2006):

nerd
    n 1: an insignificant student who is ridiculed as being affected
         or boringly studious [syn: swot, grind, nerd, wonk,
         dweeb]
    2: an intelligent but single-minded expert in a particular
       technical field or profession

The Jargon File (version 4.4.7, 29 Dec 2003):

nerd
 n.

    1. [mainstream slang] Pejorative applied to anyone with an above-average IQ
    and few gifts at small talk and ordinary social rituals.

    2. [jargon] Term of praise applied (in conscious ironic reference to sense
    1) to someone who knows what's really important and interesting and doesn't
    care to be distracted by trivial chatter and silly status games. Compare 
    geek.

    The word itself appears to derive from the lines ?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!? in the Dr. Seuss book If
    I Ran the Zoo (1950). (The spellings ?nurd? and ?gnurd? also used to be
    current at MIT, where ?nurd? is reported from as far back as 1957; however,
    knurd appears to have a separate etymology.) How it developed its
    mainstream meaning is unclear, but sense 1 seems to have entered mass
    culture in the early 1970s (there are reports that in the mid-1960s it
    meant roughly ?annoying misfit? without the connotation of intelligence.

    Hackers developed sense 2 in self-defense perhaps ten years later, and some
    actually wear ?Nerd Pride? buttons, only half as a joke. At MIT one can
    find not only buttons but (what else?) pocket protectors bearing the slogan
    and the MIT seal.


The Free On-line Dictionary of Computing (30 December 2018):

nerd

    A generally pejortive term for any person who is
   socially inept and studious or demonstrates obsessive
   knowledge of something.  For example, a computer nerd.  The
   term first appeared in print in "If I Ran the Zoo", 1950 by
   Dr. Seuss.

   Compare: geek.

   (2010-02-28)