Final answer:
Protists refer to many clades of eukaryotes that are not monophyletic. They include microscopic one-celled organisms like algae and plankton, as well as giant seaweeds.
Step-by-step explanation:
The term "protists" refers to many clades of eukaryotes that together are not monophyletic. Protists are all the eukaryotic organisms that do not fit into one of the other three kingdoms (plants, animals, and fungi). They include many kinds of microscopic one-celled organisms, such as algae and plankton, as well as giant seaweeds.