1. something that you do or take part in
2. the state of being active or busy
3. a particular form of organized action or behavior

Examples

• The children enjoyed the outdoor activities at summer camp.
• Reading is my favorite leisure activity.
• There was a lot of activity in the kitchen before dinner.
• The volcano showed signs of increased activity.
• After-school activities help students develop new skills.
• Economic activity slowed down during the recession.
• The detective noticed suspicious activity near the building.