low-grade charcoal from crude wood
Refers to charcoal produced from low-quality or unrefined wood, often used for everyday purposes rather than high-end applications like tea ceremony.
See also: 浅木
Low-grade charcoal is often used in ordinary households because it is cheap and readily available.
Compound of 浅木 (asagi, 'crude wood') and 炭 (sumi, 'charcoal'). The reading ずみ is a rendaku form of 炭 (sumi).