RELATED Returns a related value from another table.
Syntax
RELATED(column)
Parameters
Column – The column that contains the values you want to retrieve.
Return Value
A single value that is related to the current row. The RELATED function requires that a relationship exists between the current table and the table with related information. You specify the column that contains the data that you want, and the function follows an existing many-to-one relationship to fetch the value from the specified column in the related table. If a relationship does not exist, you must create a relationship.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference