The custom list of predefined values is called Enum (enumeration). The parameter can be made Optional, in which case you have to define a default value. The decriptions are called "Xml documentation" and works like special code comments that integrates with the Intellisense help system, see help topic How to: Create XML Documentation in Visual Basic
Private Enum Customlist
''' This method does nothing.
''' <param name="param">An optional option from Customlist options</param>
Private Sub Method(Optional ByVal param As Customlist = Customlist.OptionA)