`\rule`

¶Synopsis, one of:

\rule{width}{thickness} \rule[raise]{width}{thickness}

Produce a *rule*, a filled-in rectangle.

This example produces a rectangular blob, sometimes called a Halmos symbol, or just “qed”, often used to mark the end of a proof:

\newcommand{\qedsymbol}{\rule{0.4em}{2ex}}

The `amsthm`

package includes this command, with a somewhat
different-looking symbol.

The mandatory arguments give the horizontal `width` and vertical
`thickness` of the rectangle. They are rigid lengths
(see Lengths). The optional argument `raise` is also a rigid
length, and tells LaTeX how much to raise the rule above the
baseline, or lower it if the length is negative.

This produces a line, a rectangle that is wide but not tall.

\noindent\rule{\textwidth}{0.4pt}

The line is the width of the page and 0.4 points tall. This line thickness is common in LaTeX.

A rule that has zero width, or zero thickness, will not show up in the
output, but can cause LaTeX to change the output around it.
See `\strut`

, for examples.