Can we describe synthetic biological sequence data as belonging to a "species" or "taxon"? For the purpose of testing phylogenetics software, we're using synthetic sequence data (i.e., it's computer generated, and there's no actual biological organism with that e.g. DNA sequence).  For real-world biological sequence data, we would say the sequence belongs to a "species" or "taxon" (or "taxonomic group"), but this feels inaccurate since there is no actual species or taxon.

Question: Can we describe synthetic biological sequence data as belonging to a "species" or "taxon"?

I'm wondering if this is standard practice, despite the synthetic nature of the data.
Phylogenies can be made with/of non-species groups. I think "taxon" is perfectly fine. You might also consider the use of the "leaf / leaves" or "terminal" if you want to emphasise the tip nature of the organisms. Even "sequence" would be fine.

Ninja edit to my own suggestion: since you're making a phylogeny from sequences of unknown context or relationship (i.e. you can't say that they're sequences from a "species" or "OTU" or from anywhere), agnostic terms like "taxon" or "sequence" are more correct.