It's no surprise that this one pops up often in Power BI interview questions on DAX.   DAX is the language of Power BI. It stands for Data Analysis Expressions. It is a functional language, much like Excel formulas. Power BI Product team created DAX by mashing up “Excel formula Language”, “SQL Language” and “MDX Language.”  DAX is Simple, but it’s not easy. Do not try to learn It in the usual way. You need to spend time understanding the hard parts.  E.g. Syntax elements: Name of Measure is “Total Sales”. operator (=) equals sign implies its beginning of the formula and returns the result. Adds up all of the numbers in the column Sales[SalesAmount] using SUM Function All functions require one or more arguments surrounded by Parenthesis () Name of Table “Sales”  The column [SalesAmount] in the Sales table and SUM function is used to aggregate Sales.