Heat; high temperature or thermal energy (physical warmth).
暖房をつけると部屋に熱がこもる。
When I turn on the heater, heat builds up in the room.
鉄は熱をよく伝える金属だ。
Iron is a metal that conducts heat well.
太陽の熱で地面が温まった。
The sun's heat warmed the ground.
Fever; elevated body temperature (also used for the temperature reading).
子どもが熱を出して学校を休んだ。
The child had a fever and stayed home from school.
体温を測ったら38度の熱があった。
I measured my temperature and had a fever of 38°C.
発熱が続く場合は医者に相談してください。
If the fever continues, consult a doctor.
Zeal; enthusiasm or passion. Often used as '...‑heat' (〜熱) to indicate craze or keen interest (e.g., "soccer fever").
最近、サッカー熱が高まっている。
Recently, soccer fever has been rising.
彼はカメラ熱に取りつかれて、休みの日はいつも撮影に出かける。
He's obsessed with cameras and spends his days off taking photos.
仕事に熱を入れすぎて休みを忘れた。
He got so absorbed in his work that he forgot to take a break.