Bunkai means "analysis" in Japanese. In most organizations this term refers to the application that actually defines the movements in a particular sequence of the kata.
Oyo means "application" or "put to practical use. In most cases "Oyo" may or may not follow the exact movements in a sequence of kata, or there may be an additional sequence added to the motion.
These are two very different interpretations of what can happen in the kata. Remember the Bunkai defines the kata, Oyo allows a little more "artistic licence".