The terms Today Extension and widget can be used interchangeably; they both refer to a component that is present in iOS's Today View. In this chapter, the term widget is used throughout.
If you swipe down from the top of the screen to open Spotlight and swipe right after that, you're presented with the Today View. On the simulator, this view tends to look rather empty, but on your device, there's probably a lot more going on. The following screenshot shows the Today View on the simulator with a couple of widgets added to it:
Users can scroll to the bottom of this view and manage their widgets from there. They can add new widgets and remove existing ones. All these widgets have one thing in common: they provide relevant information for the current moment or day. For the Calendar, this means showing events that you have planned for today or tomorrow. The Favorites widget in the screenshot usually contains contacts that the user interacts with...