picnic blanket; leisure sheet
A waterproof or water-resistant sheet used for sitting on the ground during outdoor activities like picnics, cherry-blossom viewing, or camping. Wasei-eigo from 'leisure sheet'.
wasei-eigo (Japanese-coined English), from leisure sheet
When we go cherry-blossom viewing in the park, we bring a picnic blanket.
We spread out the leisure sheet and ate our packed lunch.