ac·ro·nym 
(ăkrə-nĭm′)
(ăkrə-nĭm′)n.
1. A word formed by combining the initial letters of a multipart name, such as NATO from North Atlantic Treaty Organization or by combining the initial letters or parts of a series of words, such as radar from radio detecting and ranging.
2. Usage Problem An initialism.
[ACR(O)- + -ONYM.]
ac′ro·nymic, a·crony·mous (ə-krŏnə-məs) adj.
Usage Note: In strict usage, the term acronym refers to a word made from the initial letters or parts of other words, such as sonar from so(und) na(vigation and) r(anging). The distinguishing feature of an acronym is that it is pronounced as if it were a single word, in the manner of NATO and NASA. Acronyms are often distinguished from initialisms like FBI and NIH, whose individual letters are pronounced as separate syllables. While observing this distinction has some virtue in precision, it may be lost on many people, for whom the term acronym refers to both kinds of abbreviations.