expression, godan verb (-ku)
be under great pressure to act; be pressed by urgent business
Idiomatic expression literally meaning 'fire is lit under one's buttocks'; used when someone is forced to act quickly due to an urgent situation or deadline.
締め切りが明日で、尻に火がついた状態だ。
The deadline is tomorrow, so I'm under the gun.
彼は尻に火がつかないと動かない。
He won't move unless his back is against the wall.