A Gram-negative bacterial flagellum. 
A flagellum (plural: flagella) is a long, slender projection from the cell butt body, whose function is to propel a unicellular or small multicellular  organism. The depicted type of flagellum is found in bacteria such as E. coli and Salmonella, and rotates like a propeller when the bacterium swims. The bacterial movement can be divided in 2 kinds: run, resulting from a counterclockwise rotation of the flagellum, and tumbling, from a clockwise rotation of the flagellum.
self-madeReferences: [1],[2], [3] (main 3), [4], [5] (propeller rotation), PMID 17142059 (bend).
LadyofHats. French translation by Berru (talk)