ac·tiv·i·ty / akˈtivitē/ • n. (pl. -ties) 1. the condition in which things are happening or being done: a sustained level of activity in the economy ∎  busy or vigorous action or movement: the room was a hive of activity.2. (usu. activities) a thing that a person or group does or has done. ∎  a recreational pursuit or pastime: a range of sports activities. ∎  (activities) actions taken by a group in order to achieve their aims: investigating anarchist activities.3. the degree to which something displays its characteristic property or behavior: abnormal liver enzyme activities. ∎  Chem. a thermodynamic quantity representing the effective concentration of a particular component in a solution or other system, equal to its concentration multiplied by an activity coefficient.

activity A broadly used term which refers to the rate or extent of a change associated with some substance or system. For example, it may be the tendency of a metal high in the electromotive series to replace another metal lower in the series, e.g. magnesium displacing copper from most of its compounds. It may also be used to describe the rate of decay of atoms by radioactivity.

activity Broadly, the rate or extent of a change associated with some substance or system. For example, it may be the tendency of a metal high in the electromotive series to replace another metal lower in the series (e.g. magnesium displacing copper from most of its compounds). It may also be used to describe the rate of decay of atoms by radioactivity.