SN2

techinically, its a bimolecular substitution reaction in which a nucleophile replaces a good leaving group. It is also known as a backside attack. this is, for example, how we can form butanol from bromobutane and HBr that was made insitu (using H2SO4 and NaBr) ((yeah dipset orgo lab...BALLL.ER)) more commonly, however, it is used to desribe what happens when studying for a final that comes back just to rape you. Hence the backside attack.