Cilia and Flagella
Cilia and flagella are tube-like appendages which allow for motion in eukaryotic cells. If a cell has a single appendage, which often looks tail-like, it is called a flagellum, but if it has many, they are called cilia. The motion of the cilia or flagellum moves the liquid outside the cell and if the cell is not anchored, it can "swim." A commonly recognized example is the "tail" on a sperm cell, which is actually a flagellum.