Every day more and more abbreviations appear, and old ones die. No sooner had we learned to refer to the Common Market as the EC rather than the EEC, than it became the EU.
Generally it is acceptable to write abbreviations either with or without full stops, but the trend is towards leaving them out, as in BBC, Dr, HoD, H E Bates, Prof E Potter. Punchy writing such as that found in advertisements tends to leave out full stops, whereas formal non-technical writing is more traditional, and full stops are often used.
There are various kinds of abbreviation. The most common is the set of initials, for example DIY for Do It Yourself, DSS for Department of Social Security, gbh for grievous bodily harm, JCB for a machine invented by Joseph Cyril Bamford.
Some abbreviations are the first part of a longer word and are pronounced as words, not said as a sequence of letters of the alphabet. Examples are ad and advert from advertisement, bra from brassière, gym from gymnasium, and limo from limousine.
Other abbreviations made by cutting off the end of the word are not used in speech, for example adv for adverb and cont for continued. If these need to be read aloud, they are read as the unabbreviated full forms.
Some words lose bits in the middle. Bdg stands for building; Chas for Charles. Dr, ft, Mr, and Mrs are other examples. These are read aloud as their unabbreviated full forms.
A few words lop off the first part, for example bus and plane, though these are now so well established that they are really no longer thought of as reduced forms, but as words in their own right.
There is a significant proportion of abbreviations which it is possible for an English speaker to pronounce as words rather than as sequences of letters of the alphabet. For example, NATO is said [nay-toe] and never [en eh tee oh]. Sets of initials like NATO, and new forms made up of the first parts of two or more words, such as OXFAM, are called acronyms. Further examples are UNESCO, Amstrad, GATT, ACORN, dinky, Aids, laser, ERNIE, and CLEAR. A few abbreviations are pronounced both ways, VAT being the prime example.
Acronyms are often new words. The word Nato did not exist before it began to be used as a quick way of referring to the North Atlantic Treaty Organization. It is not, in fact, a very typical English word, although it is easy enough for English speakers to pronounce. COHSE, the Confederation of Health Service Employees, looks un-English, but is pronounced [cosy].
Laser, on the other hand, looks thoroughly at home in English. There are probably many people who are quite unaware that it is an acronym, derived from: light amplification by stimulated emission of radiation. The fact that it is not written in capital letters, and is a common noun rather than the name of an organization, also helps to disguise it. This is the sort of acronym that easily makes its way into a dictionary. Yuppie, from: young upwardly mobile professional; and radar, from: Radio Detection and Ranging, are other examples.
Some acronyms are existing words taken over as more easily used alternatives to full forms, ACORN, for example, which stands for: A Classification of Residential Neighbourhoods, a sampling system based on different kinds of dwelling; or AIDS, from: acquired immune deficiency syndrome; or WASP, from: White Anglo-Saxon Protestant.
Some organizations deliberately choose terms for products, projects, or equipment so that the initials will make an existing name. An example of this is ERNIE, from: Electronic Random Number Indicator Equipment. This is the machine that chooses the winners of Premium Bonds. A TESSA is a Tax Exempt Savings Bond. These short and friendly-sounding names suggest something pleasant and accessible. Another case of image manipulation by acronym is the choice of the title Fast Reactor Experiment, Dounreay to give FRED.
Campaigning organizations, in particular, choose names to yield an acronym that is suggestive of their aims. ASH, Action on Smoking and Health wants people to stop smoking; GASP is the Group Against Smog Pollution; SCUM, the Society for Cutting Up Men, wants to attract your attention.
The form in which acronyms are written varies. The small number that are common nouns rather than names are often found in small letters, and become indistinguishable from words. These are nouns such as laser, radar, and aids. The plural is made, as with most ordinary words, by simply adding s, for example KOs, JCBs, lasers. No apostrophe is needed.
Names of organizations are most often written as a string of capital letters without full stops, but practice is variable, and you may see Unesco or UNESCO as well as UNESCO. You may even see U.N.E.S.C.O..
Note that not all abbreviations that could be acronyms are so in fact. BA, for example, is always said [bee eh] and never [bar]. A particularly interesting case is ETA. When it means 'Estimated Time of Arrival' it is an abbreviation, and is pronounced [ee tee eh], but when it stands for the Basque separatist group it is an acronym, and is pronounced [etter], to rhyme with better.
One problem with abbreviations that are pronounceable as words is that when you meet a new one in print, you may not know which way to say it. This is more of a problem now that all abbreviations, not just acronyms, tend to be written without full stops. A full stop after each letter usually means that the abbreviation is pronounced as a string of letters.