The term OK has been in use since 1840. It was actually a slogan of a Democratic Party political club called O.K. Club.
O.K. stands for Old Kinderhook. Kinderhook is the name of a place in New York. It was also the nickname of the then US President Martin Van Buren as he was born there. Any member of this club was usually described as an OK guy. And because the party had a positive image at the time, being an OK guy was some sort of a compliment. And as time went by, the term OK became synonymous with alright.
OK is one of the most popular words in English. It is so popular that even people who don’t know any English sometimes use it. The word OK denotes ideas such as acceptance, agreement, assent, acknowledgement, approval etc.
When you that The film was OK, what you mean is that it is a reasonably good film that most people will enjoy. OK is not used to refer to something outstanding or brilliant.
- Her performance was brilliant. (= She delivered a great performance.)
- Her performance was OK. (= Her performance was satisfactory.)
OK is sometimes also written as okay. This form is preferred when there is an inflectional ending.
- The manager okayed the purchase. (= The manager gave his assent to the purchase.)
- ‘Are you doing okay?’ ‘Sure.’
- I’m okay. How are you?