1. What does it mean?
멍때리다 describes a blank, unfocused moment when your attention drifts and you are not following a particular thought or task. You might do it while resting, waiting, or recovering from a tiring day.
Also written or said as 멍 때리다, meongttaerida
2. The nuance
It does not necessarily mean sleeping or deliberately ignoring someone. The casual question 왜 멍때려? can sound impatient, so consider the other person's situation.
3. Examples
“창밖으로 지나가는 구름을 보며 잠깐 멍때렸어.”
I zoned out for a moment watching the clouds go by outside.
“음악도 끄고 십 분만 멍때리고 싶다.”
I want to turn off the music and just space out for ten minutes.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.