To throw away means to get rid of something by putting it in the trash because you don't need it anymore or because it's broken, used up, or spoiled. When you finish eating an apple and toss the core in the garbage, you're throwing it away. When a pencil becomes too short to sharpen anymore, you throw it away.

Sometimes people use this phrase to mean wasting something valuable. A talented athlete who never practices might throw away her natural ability. A student who doesn't study for an important test could throw away a good grade. When someone says “don't throw away this opportunity,” they mean don't waste your chance to do something worthwhile.

The phrase suggests finality: once you throw something away, it's gone. That's why people get upset when someone throws away something important by mistake, like accidentally tossing homework in the trash instead of putting it in a backpack. It's also why we say a throwaway society produces too much garbage, or call something a throwaway comment when the words don't seem carefully chosen or meaningful.