noun
banked fire; live charcoal covered with ash
Refers to charcoal that is kept smoldering under ash for later use, a traditional method to preserve fire.
囲炉裏の活け炭は、朝まで消えずに残っていた。
The banked charcoal in the hearth remained alive until morning.
火鉢に活け炭をしておくと、いつでもお湯が沸かせる。
If you keep live charcoal banked in the brazier, you can boil water anytime.
Compound of 活け (ike, 'keeping alive') + 炭 (sumi, 'charcoal'), with rendaku voicing to zumi. The spelling 埋け炭 uses 埋ける (ikeru, 'to bury') to emphasize the ash-covered state.