An organism is a living thing, and there are two broad categories of organisms: those made up of only a single cell, and those made up of multiple cells.
Single-celled organisms means which contains only one cell are called unicellular organisms. 'Uni-' means 'one,' so the name 'unicellular' literally means 'one cell.'
Examples of Unicellular or Single celled organisms ::
Prokaryotic organisms like Bacteria,...
Some algae like green algae, euglena,...
