Final answer:
Diapedesis is the process allowing WBCs to move through the blood vessel walls to reach areas of infection or injury, playing a crucial role in the body's immune response.
Step-by-step explanation:
The process by which white blood cells (WBCs) are able to move in and out of blood vessels is known as diapedesis. This movement is essential for the immune system, allowing leukocytes to reach sites of infection or injury. During diapedesis, these cells are able to squeeze through the endothelial cells of the blood vessel wall to enter the surrounding tissues where they then carry out their function as part of the body's immune response.