a table covered by a quilt with a heater underneath that keeps the enclosed area warm
a table covered with a padded duvet of sorts, with a heating element underneath
A table with a heater built in underneath. The kotatsu is one of the main - and favored - ways of keeping warm during the Japanese winter. The table is covered with a blanket to trap the heat, warming your legs and any other body parts you stick underneath. The downside is that you will not want to move from the kotatsu for anything in fear of the cold waiting in the rest of your home.
A is a low, wooden table frame covered by a futon, or heavy blanket, upon which a table top sits. Underneath is a heat source, often built into the table itself.