SELECTEDVALUE Returns the value when the context for columnName has been filtered down to one distinct value only. Otherwise returns alternateResult.
Syntax
SELECTEDVALUE(columnName[, alternateResult])
Parameters
ColumnName – The name of an existing column, using standard DAX syntax. It cannot be an expression.
AlternateResult – (Optional) The value returned when the context for columnName has been filtered down to zero or more than one distinct value. When not provided, the default value is BLANK().
Return Value
The value when the context for columnName has been filtered down to one distinct value only. Else, alternateResult.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference