The command \hline in LaTeX is most commonly used in tables. It is used to make a horizontal line across the width of the table.
Examples[]
| Markup | \begin{tabular}{ cccc }
1 & 2 & 3 & 4 \\ \hline
5 & 6 & 7 & 8
\end{tabular}
|
| Renders as | 
|
| Markup | \begin{tabular}{ |c|c|c|c| }
\hline
1 & 2 & 3 & 4 \\
\hline
5 & 6 & 7 & 8 \\
\hline
\end{tabular}
|
| Renders as | 
|
Note that a double backslash \\ is required after the last row to produce a horizontal rule below the table.