<abbr> marks an abbreviation or acronym. Explain an unfamiliar abbreviation in visible text on first use, so people can understand it with a keyboard, touch screen, or screen reader.
Smallest working example
HTML and CSS
HTML
<p>Cascading Style Sheets (<abbr>CSS</abbr>) control how a page looks.</p>CSS
Edit HTML or CSS to update the preview as you type. Copy code snippet copies the selected tab. Preview spacing and font defaults are not included.
The expansion is available to everyone. The element adds semantics; its visual decoration can differ between browsers.
The title attribute
title is optional. If you include it, its value must be the full expansion, without extra commentary:
<abbr title="Cascading Style Sheets">CSS</abbr>A tooltip alone is not a sufficient explanation. Tooltips are difficult to discover on touch screens and can be inconsistent for keyboard and screen-reader users. Keep an important definition in the text.
A practical use
On a technical page, introduce an unfamiliar term once, then use the abbreviation in later paragraphs. A glossary can provide a longer definition. Use dfn where you define a term and a to link to the definition.
Common mistakes
The title on one occurrence does not apply automatically to the same abbreviation elsewhere. Do not use abbr merely to create dotted underlining; use text-decoration for appearance.
Sources and browser support
MDN: abbr describes the syntax and links to the specification and compatibility data. Check individual values in that table when supporting older browsers.