Protista is a term used to describe a group of single-celled eukaryotic organisms. Some of the synonyms for the word "protista" include Protoctista, unicellular eukaryotes, and protozoans. These organisms can be found in a variety of environments including freshwater, marine, and terrestrial. They play important roles in ecosystems as primary producers and as the basis of food chains. Some protists are pathogenic and can cause diseases in humans, animals, and plants. The study of protists, known as protistology, is important in understanding the diversity of life on Earth and their ecological roles.