Timeline is part of Windows 10’s Task View. It shows a history of activities you’ve performed and can even synchronize activities across your PCs. You can then easily pick up where you left off.
This feature is part of Windows 10’s April 2018 Update. It can also work with mobile apps if you sign into them with your Microsoft account, so you might see a Word document you opened on your iPhone or Android phone appear in the Timeline on your PC.