Final answer:
A notification allows services to display messages to users even when they are using different applications, facilitating multitasking and real-time information updates.
Step-by-step explanation:
A notification provides a way for a service to display a message even when another app is running. Notifications are essential in keeping users informed about important events, messages, or updates without the need to be inside the app that generates the notifications.
They appear in a dedicated area of a device's interface, such as the notification drawer on Android or Notification Center on iOS. As part of the operating system's functionality, notifications offer a user-friendly method of multitasking and staying connected with different apps and services.
An overlay provides a way for a service to display a message even when another app is running. It is a graphical user interface element that appears on top of the screen or other windows, allowing the service to present important information or notifications.
For example, a weather app may use an overlay to show the current temperature and weather conditions on top of other apps. This allows users to quickly access weather information without having to switch to the weather app.
Overlays are commonly used in mobile app development to provide a better user experience and ensure important information is easily accessible.