it may be no longer useful as it has served its purpose, and at the end of the process have no further use, and is generally discarded. it is unwanted material that people have thrown away. it is often also called trash, "garbage", "rubbish", or junk. it can be solid, liquid, or gas, or it can be waste heat. there are many different kinds of waste. garbage is the waste we produce daily in our homes, including old or unwanted food, chemical substances, paper, broken furniture, used containers, and other things.