An item that's thrown overboard goes into the water from a ship or boat.
When you're sailing or on a cruise, and someone drops something like a life jacket or a toolbox, it might get tossed overboard. This can happen if there's strong wind or waves, but even in calm weather, accidents can still occur. Imagine being on a small sailboat with friends, and someone accidentally lets go of the rope that's holding the cooler – it could slide right off into the drink! That's basically what it means to be thrown overboard.
To throw over the edge of a boat into the water.
Outside of a boat, in the water
Over the edge; especially, off or outside of a boat.
Example: It was their practice to throw the scraps overboard.
