Words for acronym, initialism and abbreviation
缩 in 缩写 means "to condense/ to contract" 

Acronym and initialism are both (首字母)缩写. (contracting a phrase using the first alphabet of each word in the phrase)
聯邦調查局 (Federal Bureau of Investigation) 的 (首字母)缩写 是 FBI

中央情報局 (Central Intelligence Agency) 的 (首字母)缩写 是 CIA

abbreviation is (字句)缩写 (abbreviate a phrase by omitting some part of it) ; 簡化; 簡稱 

Example: 


中央情報局 簡稱 中情局 (the abbreviation of 中央情報局 is 中情局)
美國 其實是 阿美利堅合眾國 的簡稱 (America is actually the abbreviation of United States of America)
阿美利堅合眾國 (United States of America) 的 (首字母)缩写 是 USA


The difference between acronym and initialism is,  you can read acronym as one word e.g. Mothers Against Drunk-driving = MAD. But you read each alphabet in an initialism

Basically 缩写 is a correct translation of all three terms