Abbreviations

a shortened or contracted form of a word or phrase, used to represent the whole, as Dr. for Doctor, U.S. for United States, lb. for pound.
an act of abbreviating; state or result of being abbreviated; reduction in length, duration, etc.; abridgment; summary:
His abbreviation of his famous monograph, an enormous endeavor in itself, made an excellent introduction to the volume of collected essays of which he was the editor.
a short phrase or reduced form used to represent a larger, more complex idea, situation, set of beliefs, etc.: “Freedom of speech” has become an abbreviation for a wealth of debate—and case law—about protesters’ rights.
The artist presented an abbreviation of line, plane, and curve; she creates breathtaking abstract representations of bodies you expect to leap off the canvas and start dancing.
Contemporary Examples

That is, I almost never encounter students who write “U” instead of “you” or use smiley faces or abbreviations like “LOL.”
Ben Yagoda: How I Not Write Bad Noah Charney February 12, 2013

I loved the simplicity of it, I loved the autonomy of it, and I loved the language of abbreviations that instant messaging has.
Adam Gopnik: I Didn’t Know What ‘LOL’ Meant Adam Gopnik September 2, 2013

And Luke taught me all of the abbreviations: “brb” means “be right back,” “U2” means “you too,” “g2g” means “got to go.”
Adam Gopnik: I Didn’t Know What ‘LOL’ Meant Adam Gopnik September 2, 2013

Historical Examples

The characteristic soundings are shown on the chart, with abbreviations indicating the nature of the bottom.
Nautical Charts G. R. Putnam

All the abbreviations used in this plate are readily understood.
Explanation of Terms Used in Entomology John. B. Smith

There are many other signs and abbreviations used in works on the various sciences.
Abbreviations and Signs Frederick W. Hamilton

A list of abbreviations to be used was given in the Library journal, Vol.
A Book for All Readers Ainsworth Rand Spofford

The list of abbreviations and signs in many of the principal dictionaries may be studied with profit.
Abbreviations and Signs Frederick W. Hamilton

Details about abbreviations and reconstructions are given at the end of the text.
The cforte of louers Stephen Hawes

Perhaps, after all, abbreviations were sometimes tolerable, and names like Arabella and Constantia were rather long.
The Vanity Girl Compton Mackenzie

noun
a shortened or contracted form of a word or phrase used in place of the whole
the process or result of abbreviating
n.

mid-15c., from Middle French abréviation (15c.), from Late Latin abbreviationem (nominative abbreviatio), noun of action from past participle stem of abbreviare “make brief,” from Latin ad “to” (see ad-) + breviare “shorten,” from brevis “short, low, little, shallow” (see brief (adj.)).

A shortened form of an expression, usually followed by a period. Dr. is a standard abbreviation for Doctor; MA is a standard abbreviation for Massachusetts.