Pardon me if this is a dumb question but what is the "@" before the string in the c# code below mean?

this.sqlInsertCommand1.CommandText = @"INSERT INTO [Order Details] (OrderID, ProductID, UnitPrice, Quantity, Discount) VALUES (@OrderID, @ProductID, @UnitPrice, @Quantity, @Discount); SELECT OrderID, ProductID, UnitPrice, Quantity, Discount FROM [Order Details] WHERE (OrderID = @OrderID) AND (ProductID = @ProductID)";