normal temperature; room temperature
Refers to the ambient temperature of the surrounding environment, typically around 20–25°C. Common in instructions for food, medicine, and chemical storage.
Please store this medicine at room temperature.
Please store this medicine at room temperature.
Please take it with water at room temperature.
constant temperature; fixed temperature
Used in scientific or technical contexts to mean a temperature that is kept steady, as in a thermostatic chamber or incubator.
In the experiment, it is necessary to maintain a constant temperature.
Let the butter come back to room temperature before using it.
It's dangerous to leave raw meat sitting out at room temperature.
恒温 explicitly means a temperature kept constant by artificial control (e.g. in an incubator), whereas 常温 in this technical sense just means a steady ambient level without implying active regulation.
Compound of 常 (じょう, 'normal, usual') and 温 (おん, 'temperature'). The reading is on'yomi, and the word is a straightforward Sino-Japanese coinage.