Official Answer to this question is – An interactive data exploration, visualization and presentation experience . It is one of the core component of MS Managed Self-service BI initiative. Power View, formerly known as “Project Crescent,” is an end-user focused tool ie UI that provides easy to use ad-hoc reporting and data exploration for users ranging from analysts to information workers. Reports can be created from data in PowerPivot workbooks or tabular and multidimensional (SQL Server 2014+) BI Semantic Models deployed to SQL Server 2012 Analysis Services. Running in a browser, powered by SharePoint Server 2010+, Power View enables users to present their insights through highly interactive visual presentations.
Powerview was first introduced in SQL Server 2012 and in Office 2013 release Powerview was integrated to Excel ( Powerview is not integrated with prior version of Excels). As Powerview is one of the core components in Microsoft Self-service BI initiative, it helps business analysts or business users (non-IT crowd) to build various types of BI reports without much support from IT. (Reportbuilder was the first step towards the adhoc reporting capability in SQL Server reporting service but it had lot of limitations. )
Powerview is a Metadata driven reporting solution. it connects to Analysis Services BI Semantic Model. What it means is, Powerview directly does not connect to raw data/data warehouse, it connects to BI Semantic model and model intern connects to raw data(please note that even Powerpivot has its own BI Semantic model). BI Semantic model provides analysts or users a universe from where they can create reports.
Powerview can connect to a local BI Semantic model builtin which Office 2013. When you use powerview in this mode, it has analysis service engine build into excel.