Power Pivot is an Excel add-in to perform powerful data analysis and create sophisticated data models. Power Pivot enable user to mash up large volumes of data from various sources, perform information analysis rapidly, and share insights easily.
In both Excel and in Power Pivot, user can create a Data Model, a collection of tables with relationships. The data model in a workbook in Excel is the same data model seen in the Power Pivot window. Any imported into Excel is available in Power Pivot, and vice versa.