What is an acronym?

According to Merriam-Webster's Collegiate dictionary, an acronym is: A word (such as NATO, radar, or snafu) formed from the initial letter or letters of each of the successive parts or major parts of a compound term. For example, take the first letter of each word in North Atlantic Treaty Organization and we get the acronym NATO. (NATO could also be called an initialism, more on that later.) Since acronyms are called words, their meanings are called definitions. The acronym NATO has the definition North Atlantic Treaty Organization. Not all acronyms form pronounceable words. SVP is an acronym that is not pronounceable, instead each letter is spoken. Some acronyms are formed from the first few letters of a word, instead of just the first letter. For example, the acronym MILCON has the definition Military Construction. The first three letters of each word are used to form the acronym instead of just the first letter. There is also a class of acronyms called initialisms. Initialisms are acronyms formed by the initial letters of each word. For example, IBM is an initialism for International Business Machines. All initialisms are acronyms, but not all acronyms are initialisms.