A painter's drop sheet.
When painting a room or masterpiece, it is important to avoid getting furniture and floor stained with paint, which can be difficult to impossible to get off afterwards. A drop sheet is a large sheet made of plastic or cloth that protects objects from paint, saving painters the back-breaking job of cleaning up. Sizes vary, but most are usually sufficient to protect a section of the room from ugly paint stains.
Sold in some hardware stores or found in incomplete paint projects.