$C_2{H}_{5}Br+NaOH\to C_2{H}_{5}OH+NaBr,$ the above reaction is

The reactions involving the attack of nucleophiles and substitutions of nucleophile are known as nucleophilic substitution reactions.

${\mathrm{H}}_3\mathrm{C}-\mathrm{Br}{+}^{-}\mathrm{OH}\to {\mathrm{CH}}_3-\mathrm{OH}+{\mathrm{Br}}^{-}$