The Collaborative International Dictionary of English v.0.48:

tribology \tri*bol"o*gy\, n. [tribo- + -ology.]
   the study of the effects of friction on parts of machinery
   moving in contact with each other, and of methods, such as
   lubrication, to counteract negative effects such as wear.
   [PJC]

WordNet (r) 3.0 (2006):

tribology
    n 1: the branch of engineering that deals with the interaction
         of surfaces in relative motion (as in bearings or gears):
         their design and friction and wear and lubrication