To be dead; to be lifeless. Also used figuratively for things that no longer work (e.g., a dead battery).
庭で鳥が死んでいるのを見つけた。
I found a dead bird in the garden.
あの古いパソコンはもうほとんど死んでいる。
That old computer is basically dead now.
携帯のバッテリーが死んでいるから充電して。
The phone battery is dead, so please charge it.
彼の笑顔は見えない。まるで心が死んでいるようだ。
I can't see his smile. It's as if his heart is dead.