Can anybody please help me to identify what the `N'@date` is referring to between the two set measures in the following exec statement? 

```
declare @sql nvarchar(4000), @dt datetime;

set @dt = '2015-10-01';

set @sql = N'select * from dim_person

where person_sid
in
(
select max(person_sid)  from dim_person

where [Effective_To] <= @date

group by person_id_number
)';

exec sp_executesql @sql, N'@date datetime',@dt;

```