coaster

a small, flat mat or pad that is placed under a glass or bottle to protect the surface of a table or counter from moisture, stains, or damage

A coaster is a small, flat object placed under a glass or cup to protect the surface of a table or counter from moisture or heat damage. Coasters are commonly made of materials such as cork, wood, metal, or plastic and may feature various designs, patterns, or decorative elements. They provide a practical and decorative way to prevent water rings or heat marks on furniture caused by condensation from cold beverages or hot cups.

someone who coasts

a resident of a coastal area