"Directed reaction" is a vague term, which is why you can't find a definition. Can you provide more context?
For a given reaction, where there are a number of possible theoretical products, if the reaction pathway is determined in some way by the structure of the starting material it could be called a directed reaction. Certain functional groups in the starting material can strongly favour the formation of one (or more) product(s) over the other range theoretical possibilities. Some relevant topics/key words to look into:
Regioselectivity
Stereoselectivity
Neighbouring group participation