Abbreviations and Acronyms

Do not start a sentence with an abbreviation beginning with a lowercase letter or symbol.

Abbreviations are created by the first letters of a term.

            Unidentified Flying Object, UFO

Acronyms are created by the first letters of a term and read as a word.

        National Aeronautics and Space Administration, NASA

        Acronyms are made plural by adding a lowercase s, NASAs.

Contractions--a form of abbreviation--are made by taking the first and last letters of a word.

                            Doctor, Dr.                Mister, Mr.

Avoid using abbreviations and acronyms--with the exception being for use with tables, charts, and figures.  

In MLA Style, abbreviations are discouraged within a text, unless the abbreviations are within parentheses. MLA Style prefers that formal titles such as Dr., Mrs. Miss., not be used. 

                        e.g., i.e., and etc. (Such abbreviations are not italicized.)
e.g. (“for example,") and i.e. (“that is”) are always followed by a comma. (e.g., …) (i.e., …)
etc. is not followed by a comma, unless required by the structure of the sentence (CMOS).

Spell out unfamiliar terms the first time with the abbreviations or acronyms in parentheses. All future references can simply use the abbreviation or acronym.
                            graphics interchange format (GIF) 

In AP Style, spell out unfamiliar terms each time.
                            graphics interchange format

Use a period after abbreviations ending in a lowercase letter.
            Dr.      pp.      et al.      a.m.      p.m.      No.

Do not use a period for abbreviations in all capitals.
        VP      CEO      FBI      UK      CFO      NFL

Do not use a period when letters replace a name.
                    JFK          MLK

Use a period after the initials of a name.
        John J. Pasquini          G.K. Chesterton

Abbreviate titles before a full name.
    Dr.      Gov.      Sen.      Rep.      Lt.      Mr.      Ms.      Rev.

The abbreviations for months are Jan., Feb., Mar., Apr.,  Aug., Sept., Oct., Nov., and Dec.--May, June, and July are spelled out. In AP Style March, April, May, June, and July are spelled out.  

Abbreviate junior or senior after a person’s name.
            Martin Luther King, Jr.
In AP Style, omit the comma before the abbreviation.
            Martin Luther King Jr.

The majority of stylebooks use postal abbreviations and therefore do not use periods for abbreviations of states and provinces.

            AL      FL      GA      IN      KS      CA

AP Style prefers the use of state abbreviations.

        N.H., Wash., Va.

        Alaska, Hawaii, Idaho, Iowa, Maine, Ohio, Texas and Utah are spelled out.

In MLA Style the names of countries, states, counties, provinces, territories, bodies of water, and mountains are spelled out.  Abbreviations are used in references and in postal codes.

Use periods for units of measurement.
        lb.      sq.      mi.      fl.      oz.      gal.

APA Style does not use periods for measurements, except for inches (in.).

                lb    sq    mi    fl    oz    gal

Do not use a period for academic degrees in CMOS and APA Style.
            BA      BS      MDiv      MA      PhD

For AP Style and a majority of stylebooks, periods are used for degrees.
            B.A.      B.S.      M.Div.      M.A.      Ph.D.

Either of the above styles is permissible in MLA.

Do not use a comma before the following.
        Company (Co.) Corporation (Corp.) Incorporated (Inc.) 
        Coca-Cola Co.              Chase Corp.              Time Warner Inc.

Some stylebooks add a comma before the abbreviations.

          Coca-Cola, Co.            Chase, Corp.            Time Warner, Inc.

Time

Time of day can be spelled out.

It was three-thirty.

It was four-fifteen.

We ate lunch at noon.

It was four o'clock.
 

Time expressed in a.m. and p.m. can be written in lowercase or uppercase letters: a.m., A.M., p.m., P.M. In most stylebooks, time is preferably expressed with a combination of a numeral or numerals and lowercase a.m., p.m.  
        7:30 p.m.
        7 p.m., or 7 p.m.
        3:48 a.m.
        3:00 a.m., or 3 a.m.