It is used to represent the name of a variable in a mathematical expression or in a programming context.
Normally browsers render them using the corresponding italic version of the font, although the style can be customized using CSS.
It should not be used for presentation purposes, for this you would have to use a
<span> with associated styles or if it makes sense some other specific tag such as
- Type: inline
- Self-closing: No
- Semantic value: No