煤

A phono-semantic compound composed of:

火 — semantic component meaning “fire”;

某 — phonetic component indicating the sound (매 / méi). The character originally referred to black residue produced by fire, which extended to mean coal.
Semantic development: - soot from burning; - black residue of fire; - coal as a fuel source.

석탄 (石炭) — coal (common term; not using 煤 directly)

매연 (煤煙) — soot; exhaust smoke

煤 is especially important in industrial and energy contexts, referring to coal as a major fuel.
Related characters: 炭 — charcoal; coal

煙 — smoke