1. the buttocks or rear end of a person
Usage: informal
2. the back or rear part of something

Examples

• He fell down and landed on his backside.
• She slipped on the ice and hurt her backside.
• The backside of the building faces the parking lot.
• Turn the paper over to see the backside.
• The backside of the mountain is covered in snow.
• Check the backside of the card for instructions.