water activity
Technical term in chemistry and food science; a measure of free water available for microbial growth, expressed as a ratio of vapor pressures.
Water activity is measured to evaluate the shelf life of food products.
When water activity is high, microorganisms tend to grow more easily.
含水量 (water content) is the total amount of water in a substance, while 水分活性 (water activity) indicates how much of that water is available for chemical reactions or microbial growth.
Compound of 水分 (water content) and 活性 (activity), a direct translation of the English term 'water activity'.