Sometimes called [stacked channel] but more properly [reflected channel].

[Lars H]: I don't think ''stacked channel'' and ''reflected channel'' are equivalent concepts. 
A [stacked channel] is a channel that is a modification of an existing channel; this can be done using the [chan create] API, but probably more often something like [Trf] is used. Conversely a [reflected channel] does not have to have another channel underneath. 
''Virtual channel'' would make sense as a collective term for both types of channels not existing as OS channels.