Abbrevations

Tag:
<abbr>

HTML code:
<abbr title="Cascading Style Sheet">CSS</abbr>

CSS code:
abbr[title] {border-bottom: 1px dotted #999;}
abbr[title]:hover {cursor:help;}

Meaning:
All <abbr> tags will have a bottom dotted line and when hovered over the cursor will change to a question mark and the title will show.

Exampe:
CSS