strange sql select statement

It's a webbsite using C# and ado.net to access a oracle database. Below is some piece of the sql select statement that is used and here you can see form_slag and I wonder
how this is possible. This form_slag looks like a variable. If I look at this sql select statement just before dataadapter.fill is executed I see this form_slag just as it is in the select statement below. What seems very strange to me is where is the actual value for this form_slag is a given.
This form_slag must have a value before the dataadapter.fill is executed but it has not or
it must be fetched from the database in some way that I don't understand.

Can anybody explain how this form_slag can be used in the way that it is used ?

select distinct form_nr,
'2;' as send_ro_roles,
'2;' || k.kli_klia as roles_and persons,
k.klia_namn as klient_ansvarig,
(
select distinct bizref_check_freq
from bizrulereference
where bizref_date =
(

   select MAX(bizref_date)
   from bizrulereference
   where BIZREF_FORM_TYPE = form_slag

//Tony Received on Mon Jul 04 2011 - 08:32:26 CDT