Flagella are appendages of movement for the bacterial. They emerge from the cell membrane. Not all bacteria have flagella but motile bacteria have flagella. Based on the number of flagella and also the location bacterial classification is done as below.
See the figure above for details.
♦ Atrichous bacteria: With no flagella on the bacterial cell wall. These are non-motile bacteria
♦ Monotrichous bacteria: With one single flagella.