Stereoselective or stereospecific?

Stereoselective reactions give one predominant product because the reation pathway has a choice. Either the pathway of lower activation energy is preferred (kinetic control) or the most stable product (thermodynamic control).

Stereospecific reactions lead to production of a single isomer as a direct result of the mechanism of the reaction and the stereochemistry of the starting material. There is no choice. The reaction gives a different diastereoisomer of the produc from each stereoisomer of the starting material.