We all use this one simple word many times every day, in many different contexts, without even thinking about it.

“Is that OK?”
“OK! That sounds great!”
“Oh, OK.”

But why do we use OK and not something else? According to Allan Metcalf, author of a new book on the history of OK, one reason is that it provides neutrality, “a way to affirm or to express agreement without having to offer an opinion”.

The use of OK used to be restricted to business contexts (o.k. meant that a document was “all correct”) and was associated by some people with illiteracy. Now however, it’s used by everyone in except in formal settings – speeches and reports for example. If you’re interested, it’s well worth reading the rest of the article by Metcalf over at BBC News.