A flagellum (; plural: flagella) is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The word in Latin means whip. The primary role of the flagellum is locomotion but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure. There are large differences between different types of flagella; the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion. However, both can be used for swimming.