The scientific name for a white blood cell is leukocyte. They are also sometimes referred to as immune cells, since white blood cells are the most important part of a human's immune system.
There are five main types of white blood cells. While they all help to protect the health of the body, they have different functions and look different from each other. When there are infectious disease cells, or injured cells, white blood cells are sent to eradicate or repair them. The most common leukocyte is the neutrophil, which is responsible for destroying harmful bacteria or fungi, and live just over 5 days on average.