The var element represents a variable.
This could be an actual variable in a mathematical expression or
programming context, an identifier representing a constant, a
function parameter, or just be a term used as a placeholder in
prose.

In the paragraph below, the letter "n" is being used as a
variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavors of ice cream to be available for purchase!</p>

For mathematics, in particular for anything beyond the simplest
of expressions, MathML is more appropriate. However, the
var element can still be used to refer to specific
variables that are then mentioned in MathML expressions.

In this example, an equation is shown, with a legend that
references the variables in the equation. The expression itself is
marked up with MathML, but the variables are mentioned in the
figure's legend using var.

<figure>
<math>
<mi>a</mi>
<mo>=</mo>
<msqrt>
<msup><mi>b</mi><mn>2</mn></msup>
<mi>+</mi>
<msup><mi>c</mi><mn>2</mn></msup>
</msqrt>
</math>
<figcaption>
Using Pythagoras' theorem to solve for the hypotenuse <var>a</var> of
a triangle with sides <var>b</var> and <var>c</var>
</figcaption>
</figure>

Here, the equation describing mass-energy equivalence is used in
a sentence, and the var element is used to mark the
variables and constants in that equation:

<p>Then he turned to the blackboard and picked up the chalk. After a few moment's
thought, he wrote <var>E</var> = <var>m</var> <var>c</var><sup>2</sup>. The teacher
looked pleased.</p>