Air, Atmosphere, Mood
noun
The sky energy... once known as a mystical essence that kept us from flying into space. Now we know this is the air. It can also mean atmosphere, though, because that's what a bunch of air between the earth and space is called. ここの空気はいいね！ Figuratively, this can also refer to the mood that's in the air or room, but not a specific person's mood!
くうき
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
山は空気がきれいですね。
The mountain air is so clean.
外から、つめたい空気が入ってきた。
Some cool air came in from the outside.
ちょっとは空気をよんで下さい。
Please just take the hint.