East Asian coal briquettes

East Asian coal briquettes (Japanese: 練炭, Hepburn: rentan), also known by the names yeontan (Korean: 연탄) or fēngwōméi (simplified Chinese: 蜂窝煤; traditional Chinese: 蜂窩煤, literally "beehive coal"), are coal briquettes used across East Asia for home cooking and residential home heating purposes. They were first invented in Japan, then propagated through the rest of East Asia in the early 20th century, although their usage is now uncommon in contemporary Japan and South Korea.

Source: Wikipedia — East Asian coal briquettes (CC BY-SA 4.0)