Pronunciation: (ak-tiv'i-tē),[key] —n., —pl.-ties. 1. the state or quality of being active: There was not much activity in the stock market today. He doesn't have enough physical activity in his life. 2. a specific deed, action, function, or sphere of action: social activities. 3. work, esp. in elementary grades at school, that involves direct experience by the student rather than textbook study.
4. energetic activity; animation; liveliness.
5. a use of energy or force; an active movement or operation.
6. normal mental or bodily power, function, or process.
7. Physical Chem.the capacity of a substance to react, corrected for the loss of reactivity due to the interaction of its constituents.
8. Physics. a. the number of atoms of a radioactive substance that disintegrate per unit of time, usually expressed in curies.
9. an organizational unit or the function it performs.