EARLIER Returns the current value of the specified column in an outer evaluation pass of the mentioned column.
EARLIER is useful for nested calculations where you want to use a certain value as an input and produce calculations based on that input. In Microsoft Excel, you can do such calculations only within the context of the current row; however, in DAX you can store the value of the input and then make calculation using data from the entire table.
EARLIER is mostly used in the context of calculated columns.
Syntax
EARLIER(column, number)
Parameters
Column – A column or expression that resolves to a column.
Num – (Optional) A positive number to the outer evaluation pass.
The next evaluation level out is represented by 1; two levels out is represented by 2 and so on.
When omitted default value is 1.
Return Value
The current value of row, from column, at number of outer evaluation passes.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference