The <abbr> elements represents an abbreviation and the title attribute provides a description for the abbreviation.

The default styling varies from one browser to another, but they will all indicate the abbreviation. Upon hovering over the abbreviation you can view the title attribute value.

Example

<div>
  Tim Cook is the <abbr title="Chief Executive Officer">CEO</abbr> of Apple
</div>

Result

Tim Cook is the CEO of Apple