Final answer:
Diapedesis is the process whereby leukocytes move across the endothelial layer and through the blood vessel wall.
Step-by-step explanation:
The process whereby leukocytes move across the endothelial layer and through the blood vessel wall is called diapedesis, also known as emigration. During diapedesis, leukocytes squeeze through adjacent cells in the blood vessel wall to enter the surrounding tissues.