Power BI is Microsoft's business intelligence platform for creating interactive data visualizations and reports from diverse data sources. It combines a desktop application (Power BI Desktop), a cloud service (Power BI Service), and mobile apps into an end-to-end analytics solution. Power BI uses DAX (Data Analysis Expressions) for calculations and Power Query M for data transformation, enabling both self-service and enterprise-grade analytics. The platform's strength lies in its ability to handle relationships between tables automatically while giving users control over filter context — understanding how context flows through relationships and DAX calculations is the key mental model that makes everything else click.