Power BI is a cloud-based business intelligence tool that allows users to perform data visualization and reporting through a self-service interface. It consists of various components such as Power BI Desktop for data modeling, Power BI Service for report sharing, and Power BI Mobile for access on the go. The document also covers data preparation, ETL processes, data analytics, and the differences between OLTP and OLAP systems, along with the use of DAX for calculations and creating reports.