DAX

Data Analysis Expressions

Formula language for Power BI, Power Pivot, and SSAS Tabular models.

When you'd see it: Power BI and Excel Power Pivot. DAX is the formula language for building measures and calculations.

Why it matters: DAX is the language behind calculations in Power BI, and its quirks, especially evaluation context, are the main learning curve for serious Power BI work. Strong DAX is what separates basic dashboards from real analysis.