Is there a standard name for this tree structure?

[Stefan Behnel]

Steven D'Aprano, 04.04.2010 14:10:
> I have a hierarchical structure something like a directory tree or a
> nested tree structure:
>
> Mammal
> +-- Ape
> :   +-- Chimpanzee
> :   +-- Gorilla
> :   +-- Human
> +-- Carnivore
> :   +-- Cat
> :       +-- Tiger
> Reptile
> +-- Lizard
> +-- Snake
>      +-- Cobra
>      +-- Python

Maybe not quite what you asked for, but given the names in the example 
above I would call this an ontology.

Stefan