The Timeline widget acts as your personal newsfeed on the homepage. It shows news and posts from pages, communities, events, and persons you are subscribed to. The widget can be installed anywhere you can edit the layout, but typically, it is purely located on your homepage.
There is also a Timeline app and a personal profile timeline, but they have different purposes compared to the widget. Although the widget and app share many features, like sticky or locked posts, shared permissions in administration, posts, and comments, the timeline app functions like a communication channel instead of a newsfeed. Your personal profile timeline only displays your own activities and shows posts that you have shared, posts that other users have posted on your Timeline, and posts you have created.