Indoors means inside a building or other structure with a roof and walls. When you're indoors, you're protected from weather like rain, wind, or blazing sunshine. A classroom, your bedroom, a shopping mall, and a gymnasium are all indoor spaces.

The opposite of indoors is outdoors, which means outside in the open air. Some activities work better indoors: reading in a library, cooking in a kitchen, or playing basketball on an indoor court when it's snowing outside. Other activities feel better outdoors: flying a kite, having a picnic, or stargazing on a clear night.

You might hear people say “use your indoor voice” when someone's being too loud inside a building. Indoor spaces usually call for quieter, calmer behavior than wide-open outdoor spaces where you can shout and run freely. When rain cancels your outdoor soccer game, you might have indoor recess instead, playing board games or doing crafts in your classroom.