In Deriscope terminology, a
Deriscope Type is called abstract when it can have no Deriscope Objects of its own, i.e. Deriscope Objects of which the true type is not a subtype of the Deriscope Type here.
For example the Deriscope Type
Tradable is abstract because there can never exist a Deriscope Object of which the true type is Tradable and not some other subtype of Tradable.

An abstract Deriscope Type cannot have the function
It may though have other Deriscope Functions