The two-word naming system you're thinking of is called binomial nomenclature. It's a standardized way to name species, developed by Carl Linnaeus.

Here's how it works:

* Genus: The first word is the genus, a group of closely related species.

* Species: The second word is the specific epithet, which distinguishes a particular species within the genus.

For example:

* *Homo sapiens* (humans)

* *Canis lupus* (wolves)

* *Quercus robur* (English oak)

Why not all organisms?

* Not all organisms are classified: Scientists haven't formally named every single organism on Earth.

* Classifications change: As our understanding of biology evolves, classifications are sometimes revised or updated.

* Not all organisms have a species name: Some organisms, like viruses, are not classified using the binomial nomenclature system.

So, while binomial nomenclature gives us a two-word name for many organisms, it doesn't cover them all.