An object parameter represents an object you choose on screen.
When you use an object parameter in a "When", the event triggers when something happens to the specified object. For example, when you choose “Is tapped,” the iPad is automatically chosen as the parameter for this when—which means the when implies “When the iPad screen is tapped.” But, you can change the parameter to another object or something else.
For an example, search the community for Bubble Wrap Popper. Each bubble is an object and when each bubble is tapped, it pops!