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An initialism is an abbreviation made from the initial (first) letters of a group of words (and pronounced as individual letters), like this:

B[ritish] B[roadcasting] C[orporation] BBC

Sometimes only the more important letters are included:

M[ember] [of] P[arliament] MP

Here are some more examples:

initialism full form
ATM automatic teller machine
BA Bachelor of Arts
CD compact disc
CEO Chief Executice Officer
DIY do it yourself
NSA National Security Agency
PLC Public Limited Company
PTO please turn over
UN United Nations
VAT value added tax
VIP very important person


How do we punctuate initialisms? Do we put a full stop/period after each letter?

This is largely a matter of style. Some people prefer the modern approach and use no full stop. Others take a more tradional approach and use a full stop. So CEO and C.E.O. are both acceptable. The important thing is to be consistent.

If the initial letters of the full form are capital letters, then the initialism should also use capital letters (National Security Agency → NSA). If the full form does not require capitals, then the initialism can usually be with or without capitals—it's a matter of style (please turn over → PTO or pto).

Note that some initialisms can also be acronyms. For example, the abbreviation for Value Added Tax (or value added tax) is:


We usually pronounce initialisms as individual letters—or else we say the full form.

write and say: ATM - BA - CD - CEO - DIY - NSA - PLC - PTO - UN - VAT - VIP

initialism (noun): An abbreviation consisting of initial letters pronounced separately (e.g. BBC) - Oxford Dictionaries