The rules for using a, an and the before initial abbreviations are the same as for using them before normal words.
A should be used before countable nouns that talk about one person or thing.
- a PA (Personal Assistant)
(p-ay)
An should be used before countable nouns that talk about one person or thing, and begin with a vowel sound (a, e, i, o, u).
- an NGO (Non-Governmental Organisation)
(en-gee-oh)
A or an are used before countable nouns to talk about something the listener or reader does not know about.
- a BBC employee (we don’t know which employee)
(bee-bee-sea)
The is used before countable nouns to talk about something the listener or reader knows about or there is only one of.
- The BBC (British Broadcasting Corporation/there is only one)
(bee-bee-sea)
