Say, for example, you're writing a blog in Word Online that mentions Paul Revere. You want to look up more information about Revere, or even embed a likeness of him. Unlike in the past, you won't have to leave the current screen to open a new window or application to look up that information.
With the Smart Lookup (also known as Insights) in World Online, you can simply select the word or phrase while in Editing View, right-click the selection, and then select Smart Lookup. You will then see on the right pane more information about the word or phrase. Isn't that smart?
This feature isn't available in Office Online when you're using Office 365 for business yet. It is, however, available when you're using the Office Pro Plus desktop application.