\documentclass[12pt]{article}
\usepackage{array}
\begin{document}
\begin{tabular}{ccp{2cm}p{4cm}}
$\ell$ & ::= & & \textbf{Locations} \\
& $\vert$ & $\tilde{\ell}$ & abstract location \\
& $\vert$ & $\ell_j$ & concrete location \\
\end{tabular}
\end{document}