Be careful with OK, it depends on the context. As the most recognised word in the world it it generally used for saying that you are 'Alright', how's things? OK, Thanks.
It can mean average, or poor, not so good - How was the food... It was OK
It's also used a lot as an affirmation - OK, let's go now, OK that's good for me.
A friend of mine took her new boyfriend (from Argentina) to visit her parents in Swizerland, after the meal they asked him how the food was, he said... it was OK, thinking that meant good.