Lost property; something someone dropped and left behind.
駅の改札で落し物の財布を届けた。
I handed in a lost wallet at the station ticket gate.
落し物センターにコートの忘れ物が届いていますよ。
A forgotten coat has been brought to the lost-and-found center.
道で携帯の落し物を見つけたので交番に預けた。
I found a dropped phone on the street and left it at the police box.
The act of dropping or losing something unintentionally (as in 'to drop something').
彼は外出中にしょっちゅう落し物をするので注意が必要だ。
He often drops things while he's out, so he needs to be careful.
出かける前に落し物をしていないか確認しなさい。
Check before you leave that you haven't dropped or left anything behind.