The story
Nunchi (눈치) is the Korean word for the skill of sensing what a room wants: who is tired, and when to keep quiet. It is built on nun, 'eye', and is often glossed as 'eye-measure'. The word is old. It appears in the seventeenth century, in a form written with the Chinese characters for eye and force.
Korean uses it constantly. Someone socially clumsy has no nunchi, nunchi eopda. Someone sharp has quick nunchi, nunchi ppareuda. Nunchi-chaeda is to catch on to something nobody has said, and nunchi-boda is to keep glancing at others to see how they are taking things, which can be a polite way of describing nerves.
What makes it hard to translate is that English spreads the skill across several words. Tact is about what you say, and 'reading the room' is a phrase, not a quality you can have more or less of. Nunchi is a single ability, and Korean treats it as something children can learn and adults can be judged on.
In 2019 the journalist Euny Hong published The Power of Nunchi, which introduced the word to many English-speaking readers as a kind of social sixth sense.
A scene: a team dinner in Seoul. The manager has gone quiet and keeps checking his phone. Without being asked, the youngest member of the team says it is getting late, starts the round of goodbyes and calls him a taxi. Everyone agrees afterwards that she has good nunchi.