A somewhat formal or technical term for activity, often used in scientific or academic contexts such as chemistry or physiology.
The activity of the enzyme changes with temperature.
This drug has the effect of increasing cellular activity.
lung capacity; vital capacity
Compound of 活 (katsu, 'life, activity') and 量 (ryō, 'quantity, amount'), literally 'activity amount'. The exact historical derivation is uncertain; it is a technical term likely coined in modern times.