contraction ,abbreviation的区别?谢谢!

Contraction: A word, as won't from will not, or phrase, as o'clock from of the clock, formed by omitting or combining some of the sounds of a longer phrase.
Abbreviation: A shortened form of a word or phrase used chiefly in writing to represent the complete form, such as Mass. for Massachusetts or USMC for United States Marine Corps.
Acronym: A word formed from the initial letters of a name, such as WAC for Women's Army Corps, or by combining initial letters or parts of a series of words, such as radar for radio detecting and ranging.