At this time of year it can be foggy in the mornings.
That's the cold, white water vapour in the air.
We can make an adjective - foggy, to describe this weather.
We can make a superlative - foggiest - it was the foggiest day ever. More often we use this word to describe something we don't understand or don't know.
I haven't got the foggiest idea what you are talking about. A useful phrase for English lessons perhaps!
Here is a popular British comedy (on TV for about 30 years I think)featuring a group of old men who go about wasting their time. In this episode, they meet an old friend, Foggy Dewhurst.
The drama takes place in a small Yorkshire town and you might find the local accents interesting. On the other hand, if you can't understand it you might say you haven't got the foggiest what the programme is about!