DAX is a programming language used in Power BI. It comprises of functions, operators and constants used in a formula, or expression, to calculate and return one or more values. DAX is used to creating calculated columns, measures, and custom tables. It can be used to solve a number of calculations and data analysis problems on the data in Power BI. Apart from Power BI, DAX can also be used to perform operations on data in PowerPivot and SSAS tabular models. DAX is simple and easy to learn.
The different types of functions used in DAX are-
Aggregate
Text
Date
Logical
Counting
Information
Also Refer: How do I implement row-level security (RLS) in Power BI using DAX?