na-adjective, noun which may take the genitive case particle 'no', noun
idleness; inactivity; doing nothing
Often used in philosophical or literary contexts to describe a state of non-action or letting things take their natural course, but also used more generally for idleness or lack of activity.
彼は無為のまま一日を過ごした。
He spent the whole day in idleness.
無為な時間を過ごすのも時には必要だ。
Sometimes it's necessary to spend time doing nothing.