SN2 reactions are one particular type of nucleophilic substitution where the rate is determined by both the nucleophile and the substrate. They usually have an unhindered substrate (primary or secondary), a strong nucleophile, and a good leaving group. There is also usually inversion of the stereochemistry at the carbon where the substitution takes place.
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R. H. DeWolfe and W. G. Young, Chem. Rev., 1956, 56, 753–901.
J. W. Hill and A. Fry, J. Am. Chem. Soc., 1962, 84, 2763–2769.