groundsheet

noun

1. （帐篷内铺地用的）防潮布
   a large piece of material that does not let water through that is placed on the ground inside a tent

1. （露营时用的）铺地防潮布
   A groundsheet is a piece of waterproof material which you put on the ground to sleep on when you are camping.

in AM, use 美国英语用 groundcloth

noun

1. a waterproofed piece of cloth spread on the ground (as under a tent) to protect from moisture

   Synonym:    ground cloth