The Wastes (wastelands, great wastes) in worldbuilding are an area devoid of major civilization and unconducive to human life or prosperity. Wastes may be magic in nature, toxic, or just naturally barren regions. They may be great deserts, frozen tundra, vast marshes, endless landfills or some other type of area. They may be poisonous, polluted, or home to severe storms.
When creating wastes for your fictional world, consider what people need to do in these areas to cross them or survive within them. People may scavenge wastes for useful items and supplies and they may have once been centers of ancient civilizations that now holds nothing but ruins.
Wastes are common in post-apocalyptic worlds but also make frequent appearances in fantasy.
Desert wastes may have great sandstorms while frozen wastes may feature freezing blizzards.