pocket heater; hand warmer; heater pack
Refers to a small, portable heat source, typically a disposable chemical pack or reusable warmer, used to warm hands or body in cold weather.
On cold days, I keep a hand warmer in my pocket.
Disposable heater packs can be bought at convenience stores.
fuel for a pocket warmer
Standard katakana spelling; usually written in kana.
Kanji form is rarely used; the word is almost always written in kana.
From 懐炉, a Sino-Japanese compound of 懐 “bosom; inside one’s clothing” and 炉 “brazier; heater,” literally a heater carried against the body.