Up until now, leaving a user review on an app on the Play Store was a one way dialogue. Most people would express their opinions or concerns about an app and there was no way for them to get a response from the developer.
To solve this predicament, Google has now introduced the option to allow developers to respond directly to the people who leave reviews on their apps.
If you remember, Google recently forced everyone to use a Google+ ID in order to leave a user review. With this new feature, users should probably get some sort of notification in their Google account if a developer responds to their review.
For now the ability to respond to reviews is limited to the top developers on the Play Store but is shortly rolling out to others.