Waste is unwanted materials and objects 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.

When waste is a liquid or gas, it can be called an emission. This is usually pollution (hurts plants and animals).

Waste can also be something abstract (something that you cannot touch), for example "a waste of time" or "wasted opportunities". When people use the words waste or wasted in this way, they are saying (directly or indirectly) that something has been used badly (using too much of it or using it incorrectly).