Dilbert Cartoon - Geeks, Nerds and Engineers

The word geek is a slang term, noting individuals as "a peculiar or otherwise odd person, especially one who is perceived to be overly obsessed with one or more things including those of intellectuality, electronics, gaming, etc.".

Nerd is a term often bearing a derogatory connotation or stereotype, that refers to a person who passionately pursues intellectual activities, esoteric knowledge, or other obscure interests that are age inappropriate rather than engaging in more social or popular activities.

An engineer is someone who is trained or professionally engaged in a branch of engineering. Engineers use technology, mathematics, and scientific knowledge to solve practical problems.

Source: http://en.wikipedia.org