K-pop groups usually have between 4 and 9 members. They sing in Korean, but their songs often add English words and phrases too. A single song might switch between three languages. That mix is partly why K-pop is easy for fans around the world to enjoy, even if they don't speak Korean.
The dancing is famous. Whole groups move in perfect time, like one big machine - feet, hands, and head all matching exactly. Performers practise the same routine hundreds of times before they show it on stage. Lots of K-pop fans learn the dances themselves and post videos of their own versions online.
One song called 'Gangnam Style' became the first YouTube video ever to reach a billion views. The singer, PSY, did a funny galloping dance that schools, sports teams, and even astronauts on the International Space Station copied. After that, the whole world started paying attention to K-pop.
K-pop is more than just music. It comes with colourful music videos, big stage shows, fashion, makeup and matching outfits. Fans collect 'photocards' of their favourite singers a bit like footballers collect football stickers. South Korea even has a special word - 'Hallyu' (한류) - for the way Korean music, films and TV have spread around the world.