A MONAD is a single-celled microorganism, which is a type of organism that consists of only one cell. Monads are typically microscopic in size and can be found in both aquatic and terrestrial environments. They are among the most primitive forms of life and are believed to be some of the earliest organisms to have evolved on Earth. Monads are also known as unicellular organisms and are classified into two main groups: prokaryotes and eukaryotes.