<abbr>

The <abbr> element indicates an acronym or abbreviation of a longer word or phrase. It can use the title attribute which is optional but recommended.

Syntax

Whenever the <abbr> tag is used, it should use the title attribute to convey a semantic meaning of the abbreviation or acronym.

<abbr title="">
  <!-- The acronym or abbreviation here -->
</abbr>

While using the title attribute can be semantically helpful, it is still a good practice in accessibility to spell out the word/phrase in the text the first time before applying the <abbr> tag. Some browsers also apply default styling to the <abbr> tag like dotted underlines or translating the text into small letters.

Example

<p>
  Tomorrow I'll be heading to the Kennedy Space Center to learn about the
  National Aeronautics and Space Administration (NASA). Touring through the
  rockets used in
  <abbr title="National Aeronautics and Space Administration">NASA</abbr>
  will be such fun!
</p>

When the mouse moves over the element, the information written inside the title attribute on a tooltip is displayed.