An amoeba is a single-celled organism that belongs to the group of protists, characterized by its irregular shape and ability to change form through the extension of pseudopodia, or "false feet." Amoebas are found in various environments, including freshwater, saltwater, and soil, and they primarily feed on bacteria, algae, and other small organisms through a process called phagocytosis. They play a significant role in the ecosystem as decomposers and as part of the food web. Some species of amoeba can also cause diseases in humans, such as amoebic dysentery.