An activity is a specific type of action or event.
Agents often use the term activity to represent socially shared events.
Activity is a [key
Because an activity is a type of action, it may include many variable instances which meet the definition of that type. (For example, getting exercise is an activity which might include instances of walking, swimming, yoga or weight training, etcetera, and weight training is an activity (at a different hierarchical level) which might include instances of squats or bench presses, etcetera.)
Agents sometimes define activities in static terms, such as maintaining specific resources in practical stasis. This is because maintenance can require agents to apply many specific actions to potentially damaging forces. (Maintenance is active support.)