It is a way of calling the student over-applied, without another occupation and therefore with little social treatment. The term extended to any erudite person in an academic, technological or any unpopular subject, but always with difficulties to relate socially. In principle it was derogatory, but today they are accepted almost as an urban tribe so it is already an adjective of belonging [as a detail, 'nerd' is invariable, with unde marked gender, while its Spanish versions as nerdo or the nardo lunaph have male and female]. The word is first mentioned in the poem "If I Ran the Zoo" ("If I ran the zoo", Dr. Seuss, 1950) where it is an animal imagined by the protagonist Gerald, without much more description. It is not certain that it is the origin, but as early as 1951 the term 'nerd' was used in American schools to qualify the student introverted and dedicated to study; that's why it's assumed that it has an English slang origin.