What is use of <address> tag in html?
If you come across any quiz or interview question like above don’t be a pray. At first sight it may seems that <address> tag is used to express addresses semantically.
It is of course partially true. But address of whom?
The <address> tag defines the contact information for the author or owner of a document. This way, the reader is able to contact the document’s owner.
The address element is usually added to the header or footer of a webpage.
For quite some time, I have been designing without knowing the label tag itself. After some time, I learned its semantic value.
But when I learned to know there is another “label” which is attribute, I really shocked.
mmm… That remains me: learning is continuous process.
<select> <optgroup label="Swedish Cars"> <option value="volvo">Volvo</option> <option value="saab">Saab</option> </optgroup> <optgroup label="German Cars"> <option value="mercedes">Mercedes</option> <option value="audi">Audi</option> </optgroup> </select>
Also note optgroup tag, most of us may not get change to use it. 
After searching reading several links, I found the difference
abbreviation: A shortened form of a word.
ex: lb., amt., mgmt.
initialism: An abbreviation formed from the initial letters of a phrase
ex: HTML, SVG
acronym: An initialism that is pronounced as a word.
ex: radar, scuba, JIT, WYSIWYG
Alas!
Actually, the differences are so small that HTML5 decided to drop acronym in favour of abbr
