Meʻamoʻuimuʻa/en

Protists (first living) are in biology one of the 4 kingdoms of multi-celled based life. In some way it is a rubbish collection, containing all organisms not yet included in the plants, animals and fungi. By consequence biologists heartily disagree with each other about them, and the exact list of members changes all the time. Mostly the protists are one-celled organisms, but there are some larger multi-celled organisms, especially the seaweeds.

The kingdom of celled living creatures
'other' organisms, most single cell (Latin: protista)
fungi (fungi)
animals (animalia)
plants (plantae)
Other organisms without distinct cells: bacteria, viruses, and so forth.

There are many different species falling under the protists, most of them only visible under the microscope. Better known are the few largers ones, the algae and seaweeds.
It is customary to distinguish 4 (or even more) algae according to their colour appearance:
green algae or seaweeds chlorophyta - belongs to the plants
blue algae or seaweeds cyanobacteria - belongs to the bacteria as it does not have cells
red algae or seaweeds rhodophyta - real protist
brown algae or seaweeds phaeophyta - real protist, most of the larger seaweeds
Evidently only the red and brown algae are belonging to the kingdom of the protists. Yet from time to time biologists group them together is a new kingdom (independent or not), the chromalveolata or chromista (coloured algae), and sometimes they do not.