The <abbr> tag comes from "abbreviation". It defines an abbreviation or an acronym, like "Mr.", "Dec.", "ASAP", "ATM".
This element is used to create an abbreviated text and it is generally used along with "title" attribute to explain the abbreviation.
An abbreviation and an acronym are both shortened versions of something else. Both are often represented as a series of letters.
You can provide information by using this element to browsers, translation systems, spell checkers and search engine indexers which is so important today for a website.
The <abbr> tag comes in pairs. Which means that the tag has opening (<abbr>) and closing (</abbr>) tags.
<html> <body> <p>Armenia is willing to join the <abbr title="European Union">EU</abbr></p> </body> </html>
To see the result bring your mouse cursor over the "EU" :
Armenia is willing to join the EU
This tag uses the Global Attributes.