Predictive Analytics analyzes historical data in order to forecast the future. The differentiator is the way data is used.
In standard HR analytics, data is collected and analyzed to report on what is working and what needs improvement. In predictive analytics, data is also collected but is used to make future predictions about employees or HR initiatives.
This can include anything from predicting which candidates would be more successful in the organization, to who is at risk of quitting within a year.