Entry from OED Online

Forms: 19- gnurd, nard, nerd, nurd. [Origin uncertain and disputed (see below).
  Perh. < nerd, a fictional animal in the children's story If I ran the Zoo (1950) by ‘Dr. Seuss’, depicted as a small, unkempt, humanoid creature with a large head and a comically disapproving expression. Alternatively, sometimes explained as a euphemistic alteration of TURD n. (see e.g. D. L. Gold in Comments on Etymol. (1983) 12 27), although given the predominance of early spellings in -e-, this seems unlikely. The suggestion that the word is back-slang for DRUNK n. is also unsupported by the spellings, as is derivation from the name of Mortimer Snerd, a dummy used by the U.S. ventriloquist Edgar Bergen in the 1930s (see e.g. J. E. Lighter Hist. Dict. Amer. Slang (1977) s.v. Nerd).] 

    An insignificant, foolish, or socially inept person; a person who is boringly conventional or studious. Now also: spec. a person who pursues an unfashionable or highly technical interest with obsessive or exclusive dedication.
 
  1951 Newsweek 8 Oct. 28 In Detroit, someone who once would be called a drip or a square is now, regrettably, a nerd. 1957 Sunday Mail (Glasgow) 10 Feb. 11 Nerda square. 1971 Observer 23 May 36/3 Nerds are people who don't live meaningful lives. 1983 Truck & Bus Transportation July 129/1 When loose-brained nurds crack up the top arrangements of a man o' my calibre, I got no union t' thump them nurds with. 1993 Sci. Amer. Apr. 96/1 ‘Nerd’..is movie shorthand for scientists, engineers and assorted technical types who play chess, perhaps, or the violin. 2002 Chicago Tribune 20 Jan. IV. 7/1 Among Silicon Valley nerds, chip engineers..are the geekiest of all.