1.
to read the room, to pick up on the atmosphere
To sense the mood or unspoken feelings of those around you and act appropriately. A key social skill in Japanese culture.
空気読んでよ。
Read the room, will you.
Cultural note
Sensing the mood of a group and acting accordingly (空気を読む) is considered a basic social skill in Japan. Someone who fails at it is 空気が読めない; the abbreviation KY (Kuuki Yomenai) was a buzzword around 2007 and now sounds dated.
Usage
The headword drops を, as casual speech often does: 空気読んで. Writing and careful speech use the full form 空気を読む.