Since many years ago (at least 5 years ago) one of the topics people have been talking about is 미세 먼지 (fine dust), which is caused by pollution. This is usually not a problem for visitors to Korea, as you can't see it in the air and it's not year round. Also it's usually not a problem to most people unless they're sensitive to air quality.
But when is there more or less fine dust in the air? Typically once the winter has ended, Korea will get a period of days where the air quality is lower due to this fine dust. Once the weather cools down again, the fine dust seems to gradually go away again.
Because of this, a new phrase was invented - 삼한사미. This phrase can be used to describe the fine dust in Korea as it comes and goes with the cold weather. I explain it in detail in this new video on my channel.