Something that happens to an app either through the action of the user (e.g., clicking a button, touching the screen, moving the phone) or through some other real world action (e.g., receiving a text message or phone call).
A software element that responds to an event, such as the when Button.Click block in App Inventor.
Writing apps where the control of the app depends on how it responds to various events..
Mobile devices are designed to constantly listen for events to occur and then to respond to those events.
A Graphical User Interface (GUI) is one that contains windows, buttons, and other components that the user can use to interact with an application.
Software, such as the Android or iOS operating systems, that intermediate the interaction between mobile apps and the underlying hardware.