ISFILTERED Returns TRUE when columnName is being filtered directly. If there is no filter on the column or if the filtering happens because a different column in the same table or in a related table is being filtered then the function returns FALSE.
ColumnName – The name of an existing column, using standard DAX syntax. It cannot be an expression.
TRUE when columnName is being filtered directly.
columnName is said to be filtered directly when the filter or filters apply over the column; a column is said to be cross-filtered when a filter applied to another column in the same table or in a related table affects columnName the column by filtering it as well.
The related function ISCROSSFILTERED function (DAX) returns TRUE when columnName or another column in the same or related table is being filtered.