User defined datatype

Hi

I have a pre existing code in an stored pro that receives multi valued  parameter from SSRS 2008.

Declare @tbl_x table(typename nvarchar(100))
While len(@rpt_parameter) >0
Begin
Insert into @tbl_x
.....
)

I'm not familiar with user defined data types and need to do same thing for a parameter of type unique identifier.
Are the variables ( in the example above: typename) defined here in the code? Do I need to do the same for unique identifier data type?
Thanks