Wiktionary
n. (context meteorology English) The altitude at which the temperature of the atmosphere is 0°C at a specific location
Wikipedia
The freezing level, or 0 °C (zero-degree) isotherm, represents the altitude in which the temperature is at 0 °C (the freezing point of water) in a free atmosphere (i.e. allowing reflection of the sun by snow, etc.). Any given measure is valid for only a short period of time, often less than a day.
Above the freezing altitude, the temperature of the air is below freezing. Below it, the temperature is above freezing. The profile of this frontier, and its variations, are studied in meteorology, and are used for a variety of forecasts and predictions. Whilst not given on general weather forecasts, it is used on bulletins giving forecasts for mountainous areas.
Usage examples of "freezing level".
The temperature has been rising steadily almost a degree per day since then and, at that rate, will cross the freezing level within two more weeks.