This kingdom is a broad category that includes all prokaryotic organisms, which are single-celled organisms that lack a nucleus and other membrane-bound organelles.

However, it's important to note that the classification of living organisms is constantly evolving. Some modern classification systems place bacteria into their own separate domain called Bacteria, alongside Archaea (another group of prokaryotes) and Eukarya (which includes all organisms with a nucleus).

So, while Monera is a traditional classification that still holds some relevance, the current understanding often places bacteria in their own distinct domain.