Which among the following is benzylic halide?

A benzylic halide features a halogen atom bonded to an $\mathrm{sp}^3$-hybridized benzylic carbon, which is the carbon attached directly to an aromatic ring.

In $\mathrm{C}_6\mathrm{H}_5{-}\mathrm{CH}_2{-}\mathrm{X}$, the halogen is bonded to an $\mathrm{sp}^3$ carbon that is benzylic. This matches the definition.

$\mathrm{C}_6\mathrm{H}_5{-}\mathrm{X}$ is an aryl halide, with halogen attached to $\mathrm{sp}^2$ aromatic carbon.

$\mathrm{C}_6\mathrm{H}_5{-}\mathrm{CH}{=}\mathrm{CH}{-}\mathrm{X}$ is a vinylic halide, with halogen on $\mathrm{sp}^2$ vinylic carbon.

$\mathrm{C}_6\mathrm{H}_5{-}\mathrm{CH}_2{-}\mathrm{CH}_2{-}\mathrm{X}$ has a halogen on a non-benzylic $\mathrm{sp}^3$ carbon.

The benzylic halide is $\boxed{A}$.