# What is the meaning of the name "S"_N2?

${S}_{N} 2 \text{ Substitution nucleophilic bimolecular}$
The rate determining step of such a reaction depends on the concentration of both substrates; i.e. it is an associative (bond-making) reaction as opposed to the dissociative (bond-breaking) mechanism of ${S}_{N} 1 \text{ (Substitution nucleophilic unimolecular)}$