Full FormsHow to write abbreviations correctly
Small points of writing make a letter or an answer look careful. These are the conventions followed in most Indian and British English writing today.
Capitals
Initialisms and acronyms made from the first letters of names are written in capitals: CBSE, RBI, UNESCO. Units of measurement are not: km, kg, cm, ml. A few keep small letters by convention, such as PhD, BSc, kWh and pH. Copy these exactly, because changing the case can change the meaning: MB is a megabyte and Mb is a megabit.
Full stops
Modern style leaves out the full stops in initialisms: write CBSE, USA, MBBS, not C.B.S.E. The same goes for titles that end with the last letter of the word: Dr, Mr, Mrs. Latin short forms written in small letters usually keep their stops: e.g., i.e., etc. Whatever you choose, be consistent within one document.
Spell it out the first time
In a report, essay or letter, write the full form the first time and put the short form in brackets: "the Reserve Bank of India (RBI)". After that use the short form alone. Very familiar ones, such as TV or ATM, need no introduction. In an examination answer this habit also shows the examiner that you know the full form.
Plurals
Add a small s with no apostrophe: ATMs, MLAs, PDFs, CEOs, two PhDs. An apostrophe shows possession, not a plural: "the CEO's decision", "the MLAs' meeting". Units never take an s: 5 km, 10 kg, not 5 kms.
A or an?
Go by the sound of the first letter as you say it, not by the letter itself. Letters that begin with a vowel sound, A, E, F, H, I, L, M, N, O, R, S and X, take "an": an MLA, an FIR, an SMS, an MBA, an HR manager. Others take "a": a CBSE school, a PDF, a UPI payment. For acronyms said as words, go by the word: a NASA mission, a NEET rank, an ISRO scientist.
Do not say it twice
When the last letter already stands for a word, adding that word again repeats it: ATM machine, PIN number, LCD display, HIV virus, PDF format, CNG gas. These are so common in speech that nobody will object, but in formal writing use the short form alone.
The and no the
Initialisms said letter by letter usually take "the" when they name one organisation: the RBI, the UN, the CBI. Acronyms said as words usually do not: NASA, ISRO, UNESCO, SEBI.
Where short forms do not belong
Chat short forms such as BTW, LOL, IDK, u and pls have no place in applications, answer sheets or emails to people you do not know well. Even in office mail, keep to the ones everyone knows, such as FYI and ASAP, and avoid inventing your own.
At the start of a sentence
A sentence may begin with a capital initialism: "GST replaced several older taxes." Avoid beginning a sentence with a small-letter short form such as "e.g." or "pH"; turn the sentence around.