Microsoft introduced the sql_variant data type in SQL Server 2000. You can use the sql_variant to store data of an unspecified or inconsistent type. Or to store data of almost any SQL Server data type. This is very useful for an input parameter for a stored procedure that can handle many different data types, or a column in a table with heterogeneous data.
More information about the sql_variant data type could be found here.
Telerik Data Access provides support for the sql_variant data type. In order to use such a column, the column needs to be mapped to a persistent field of type object.