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
Actually, the differences are so small that HTML5 decided to drop
acronym in favour of