The Collaborative International Dictionary of English v.0.48:

yuppie \yup"pie\, yuppy \yup"py\(y[u^]p"p[y^]), n. [young urban
   professional + -ie.]
   an ambitious young adult, usually college-educated, living in
   or near a large city, with a professional career and an
   affluent lifestyle. The "u" in the word is sometimes
   interpreted as meaning "upwardly mobile".
   [PJC]

WordNet (r) 3.0 (2006):

yuppie
    n 1: a young upwardly mobile professional individual; a well-
         paid middle-class professional who works in a city and has
         a luxurious life style