There is a shop in almost every neighborhood that specializes in custom-made tarps called 천막 (天幕 in Chinese characters). Various colors and patterns of tarp are available, and the shop will cut it to the size that you want, and insert holes with metal rings as you like. The tarps are widely used for everything from covering up a shop’s wares on the sidewalk, after the business is closed (there seems to be less concern about theft or vandalism) or on a rainy day. Also, the tarps are used for constructing temporary sidewalk restaurants called 포장마차 (pojang-macha).
The truck below is selling fruit out of the back. A 천막 has been set up to keep the back covered.