Here's the breakdown:

* One-celled organisms: These are organisms made up of only a single cell, also known as unicellular organisms.

* Without a nucleus: This means the genetic material (DNA) isn't enclosed within a membrane-bound nucleus. Instead, it's located in a region called the nucleoid.

The Monera kingdom was a broad classification that included bacteria and archaea. However, modern taxonomy has separated these into two distinct domains:

* Bacteria: These are prokaryotes found in diverse environments, from soil to the human gut. They can be beneficial (e.g., in digestion) or harmful (e.g., causing infections).

* Archaea: These are also prokaryotes but are often found in extreme environments like hot springs or salty lakes. They have unique biochemical pathways and are closely related to eukaryotes (organisms with a nucleus).

While the term "Monera" is no longer used in modern classification, it's still helpful to understand that it encompassed the diverse world of single-celled organisms without a nucleus.