Generally regioselective and stereoselective reactions are same, i.e. A reaction in which a reactant gives 1 compound in higher yield than the other. If the product is a stereoisomer then it is stereoselective and if it is not then regioselective reaction.(E.g.:-Markownikoff addition to propene is regioselective and to styrene is stereoselective)

 

In a stereospecific reaction one stereoisomer will give another stereoisomer in higher yield(e.g.:- ANTI addition of Br2 on cis-2-butene). Whereas in regiospecific reactions the product is not chiral.