An abbreviation (from the Latin, brevis, meaning short.) is a shortened form of a word or phrase used almost exclusively in print. For example:

LOL = laugh out loud
mins = minutes
abbrv = abbreviation

As you can see, abbreviations are often either the full word shortened or the first letter of each word in the phrase (aka acronyms). They can contain letters and numbers, upper and lowercase.

BBI5 = be back in 5 minutes
PhD = doctor of philosophy

In a very few cases the abbreviation is more commonly used than the original full length phrase which (in some cases) is virtually never used, for example:

etc. = et cetera
e.g. = exempli gratia
i.e. = id est

Abbreviations have been used since the earliest form of writing. With the rise of literacy they became more commonplace and during the Victorian era the number in common use grew massively in print. However, with the recent surge in IMing (Instant Messaging) the number of abbreviations has grown even more. Some of these are somewhat obscure and only used by those in the know. (Famously the British PM, David Cameron, used LOL thinking it meant lots of love – or so he said.)

As for their use, there are no hard and fast rules about where abbreviations are used. Most are to be found in informal writing but some, often the name of organizations or Latin phrases, can be found in formal writing. Perhaps the most common place to find them these days is on the internet in places such as Twitter where writing space is at a premium.

Abbreviations with a Period or Full Stop

Again there are no hard and fast rules when to use a period or full stop at the end of an abbreviation. In American English‏‎ there is a tendency to use one, in British English there is a tendency not to. A lot of people use a period or full stop only when the last letter of the full word or phrase is not used.

So, for example, the following abbreviations which begin with the first letter and end with the last letter do not have a full stop:

Mr = mister
Dr = doctor

But…

etc. = et cetera
e.g. = exempli gratia
i.e. = id est

Having said this, you will doubtless see plenty of examples where they are written differently.

Abbreviations in Plural

To make the plural of an abbreviation, simply add -s to the abbreviation. This is almost always lowercase.

Drs = doctors
MPs = members of parliament

Abbreviations in the Classroom

Abbreviations should be taught as a whole along with the full word or phrase they represent. It is not really useful to teach them in groups, but rather as simple vocabulary items as and when they are needed.

Useful Links

There are many thousands of abbreviations in common use and new ones are being coined every week. You can find a massive repository of abbreviations at Abbreviations.com which contains hundreds of thousands of them.