Wasteful means using more of something than you need, or using it carelessly so it gets thrown away without serving its purpose. When you take three pieces of paper to draw one picture and toss the others in the trash, that's wasteful. When a factory dumps chemicals that pollute a river instead of properly disposing of them, that's wasteful too.

Being wasteful usually means not thinking carefully about resources. A wasteful eater might pile their plate high at a buffet, then leave half the food uneaten. A wasteful driver might leave their car engine running for twenty minutes while parked. Wasteful habits cost money, use up materials others could have used, and often harm the environment.

The opposite of wasteful is efficient or thrifty: using just what you need and making the most of it. Thomas Edison tested thousands of materials before finding the right filament for his light bulb, but he wasn't being wasteful because he learned something from each attempt. That's different from throwing away something useful without caring or paying attention to what you're using up.