Powerpivot is a function that allows pivot tables to get one step better, making it possible to combine and summaries data from across multiple different sheets without VLOOKUPs. Essentially, it’s another free Add-In from Microsoft, with the ability to transform Excel into a much more powerful beast – think pivot tables, but with much more power. You can activate Powerpivot, which presents as a new ribbon tab, by clicking File>Options>Add-Ins and choosing to manage your Excel Add-Ins. From there, it’s a case of selecting Powerpivot and confirming to activate this functionality.
https://support.office.com/en-nz/article/Power-Pivot-Add-in-a9c2c6e2-cc49-4976-a7d7-40896795d045