The term “Kuudere” refers to a Japanese character type in anime and manga.
A “Kuudere” (or sometimes written as just “Kudere”) person is cold, blunt, cynical and usually shows no emotion to the ones who they care (liking or loving) for on the outside, but on the inside they are caring and nice to them.
They only speak a few words in a calm and monotone way, and they don’t show any emotion.
In a few extreme cases, they seem to be completely emotionless to the others, however they always appear as calm and composed.
It might seem like they are acting seriously on the outside, but this is often accompanied by a sarcastic sense of humour.
The term “Kuudere” started to appear outside of Japan at the same time, when the anime and manga culture was released to the western audiences in around the 1990s.
The exact origin of the term is unknown, however on the internet it has started to spread after the first anime/manga was introduced, featuring a “Kuudere” character.
Since it’s originality and popularity of the way of “Kuudere” people and characteristics in the Japanese culture, the term was already very popular in the mainland, however it has gained a huge boost in popularity when the western world embraced the culture in the form of anime and manga material.