Tag Description
<abbr> Abbreviations, when used, need to be marked so that the user is able to find the meaning of it, in the event they do not know it. When the user hovers over the abbreviation, a tooltip should pop-up giving the expanded form of the abbreviation.

Example:

HTML Code Display
The <abbr title="World Health Organization">WHO</abbr> was founded in 1948. The WHO was founded in 1948.