Abbreviations are the shortened form of a word or phrase. For example, “Sat.” is an abbreviation for “Saturday.” Most commonly used abbreviations are official, and they are easily found in an online dictionary should you find a word where you are unsure of the proper abbreviation. Some words are sometimes abbreviated in multiple ways. Abbreviation is shorted to “abbr.,” “abbrv.” or “abbrev.,” for example. Some miscellaneous abbreviations require periods at the end (etc.) or an “s” to show the plural form (“vols.” for volume); others do not require either (“pp” = page or pages, 9 mg = 9 milligrams).
Abbreviations are rarely used in formal and professional writing, so you should strive to avoid using them unless the scope of the content is very informal. An exception is abbreviations that are used for common titles, such as Dr. (doctor), Mr. , Mrs., or Ms.; although the final three listed here are not actual abbreviations for a longer word, they are usually grouped in this category. Likewise, abbreviations for time (a.m. and p.m.) and dates marking periods before or after the birth of Christ (a.d. and b.c) are acceptable in all types of writing as well. Other acceptable miscellaneous abbreviations for more formal writing include “e.g.” (for example), “i.e.” (in other words), “et al.” (and other people). Use these with caution, though, and ensure they are appropriate for your specific writing task. They are acceptable for an article, blog post or essay, but they are inappropriate for a product description.
Acronyms are a subset of abbreviations. While they are a shortened form of a word, acronyms form a word from the beginning letters, syllables or parts of a name or phrase. An acronym forms a new word and is usually, but not always, in all capital letters. “NATO” for example, is an acronym for the North Atlantic Treaty Organization. Acronyms are formed using the only the initial letters, as is the case with “NATO” and “scuba” (self-contained underwater breathing apparatus); others are formed using a combination of the first letters and some of the following ones from particular words, as is the case with “radar” (radio detection and ranging).
Initialisms are another subset of abbreviations. They differ from acronyms in that they do not form new words. Instead, the first letter of each word from a name or phrase is used with each letter pronounced (or read) separately. Whether the periods are necessary for grammatical correctness is not official in most cases, so if you are unsure, you should attempt to look up the most common way one is used to make a determination. For example, “US” or “U.S.” is an initialism for United States. The initialism for United States is somewhat unique, though. When used as a noun, it can appear as US or U.S.; however, when used as an adjective, is should appear as “U.S.” Consider the following example:
The United States is a large country, and there are more than 400 United States Congressional Districts.
The US (noun) is a large country, and there are more than 400 U.S. (adjective) Congressional Districts.
The key difference between acronyms and initialisms is that one creates a new word and one is simply a series of letters that are read separately. Both of these types of abbreviations are more acceptable in formal and professional writing. When using ones that are very common, such as U.S. or AIDS, it is not necessary to provide the full, spelled-out version of the abbreviation. However, for more obscure types of these abbreviations or those that are not common knowledge, it is best to first use the full version with the shortened form in parentheses immediately following. After this initial use, it is okay to switch to the abbreviation periodically. In fact, this helps make any piece a bit more readable by providing alternative phrasing. Consider the following:
NATO is an acronym because it is spoken as a word (nay-to).
FBI (Federal Bureau of Investigation) and MIT (Massachusetts Institute of Technology) are initialisms because the letters are pronounced individually (F-B-I and M-I-T).
Example for formal/professional writing:
First use: The Federal Bureau of Investigation (FBI or F.B.I.) is driven by intelligence gathering to enforce the law and provide national security.
Second use: The FBI has existed for more than 100 years.