Some bacteria have flagella (singular, flagellum) which are tail-like appendages that allow bacteria to propel themselves.
In eukaryotes, cilia and flagella are hairlike projections that can move either stiffly, like an oar, or in an undulating fashion, like a whip.
Def: flagellum - plural, flagella. Long slender extension sued for locomotion by some bateria, protozoans and sperm. 53, 65, 274