Gentle pushes, or reminders, that play on psychological factors, motivating the user to take action.
In an eCommerce context, nudges can be seen, for example, with a pop-up that displays, notifying the shopper only three more items are left in stock, for example.
This “nudge” motivates action because it creates a sense of urgency. The shopper must buy before the remaining supplies are gone.
The shopper has been nudged to take action and convert.