An amoeba, sometimes written as "ameba", is a term generally used to describe a single celled eukaryotic organism that has no definate shape and that moves by means of pseudopodia. Pseudopodia or pseudopods are temporary projections of the cell and the word literally means "false feet". The cell uses the pseudopodia as a means of locomotion. The plural of amoeba is "amoebae", not "amoebas". Although the word "amoeba" or "amoeboid" is often used to refer to all protozoa that move using pseudopodia, the word Amoeba (written in italics and with a capital letter) refers to a specific genus of protozoa of which Amoeba proteus is the best-know species.

The cytoplasm of an amoeba contains the organelles and is enclosed by a cell membrane. An amoeba uses a process called phagoctyosis to obtain food. This is a process in which projections of the cell membrane of the amoeba extend and surround the food particle, totally enclosing it. The food particle is thus internalized in a sort of "bubble" called a vacuole. The food particle can then be digested in the vacuole. The amoeba reproduces via mitosis.

Some amoebae can cause disease. For example Acanthamoeba can cause amoebic keratitis and encephalitis in humans.