Abbreviations come in three flavours. Vanilla, strawberry, and chocolate. Well, not really. But otherwise it’s too boring. Let’s start with the vanilla ones.
This is probably what you first thought of when you read abbreviations. It is a short version of a long word. Some examples:
Lieut. = Lieutenant
Tues. = Tuesday
cent. = century
There’s not much to say about these, except to mention that a full stop replaces the missing letters.
Initialism, yes it is a word. You use the first letter of each word instead of writing the whole word. Examples:
In British and technical English, you don’t need to add full stops, if there is more than one capital letter, i.e. UK, not U.K.
Exactly the same as initialism, except that the letters themselves create a word that you can say. Examples:
Note the difference. You cannot make a word from CIA, BBC. You could make a word from UN, but nobody would know what you are talking about.
As above, you don’t need to add full stops to indicate the missing letters when there is more than one capital letter. For example, UEFA, not U.E.F.A.
SIO (Spell It Out)
Initialisms and acronyms drive me crazy when they are not spelled out. Including the ones you think are simple. Never assume that your reader will know what you mean, and always make it as easy as possible for them to find out. Sometimes this will entail providing a glossary, other times you just need to SIO (spell it out) as you go along.
Bear in mind that abbreviations are culturally dependent. The BNP means two very different things to a French person and a British person. The French person will assume you are talking about the bank, BNP Paribas, while the first thing the British person will think of is the British National Party, a right-wing political organisation.