Refers to charcoal as a material, fuel, or drawing medium. Common in cooking, heating, and art contexts.
We use charcoal for the barbecue.
He drew a sketch with charcoal.
charred remains
Rare use for something that has been burned to charcoal-like remains, such as after a fire.
After the fire, the house was like charred remains.
My grandfather made his living by making charcoal in the mountains.
We lit the charcoal before the barbecue.
Fish grilled over charcoal has a wonderful aroma.
The pillars of the house were burned to charred remains in the fire.
灰 is ash, the powdery residue left after something burns completely, whereas 炭 (in its 'charred remains' sense) still keeps a solid, blackened form.
partly burned charcoal; charcoal that has been extinguished · servant boy at a brothel or teahouse (archaic)
cut-up charcoal; charcoal pieces