charcoal briquette
A traditional Japanese fuel made from charcoal powder pressed into a round or oval shape, often used in hibachi or kotatsu. Now somewhat old-fashioned.
In the old days, people used charcoal briquettes in a hibachi during winter.
Standard kanji spelling for this traditional charcoal briquette.
Compound of 炭 (sumi, 'charcoal') and 団 (dan, 'round mass, lump'). The reading たどん is a sound shift from たんだん.