What is "diapedesis"

Diapedesis \Di`a*pe*de"sis\, n. [NL., fr. Gr. ? a leaping or oozing through, fr. ? to leap through; dia` through + ? to leap.] (Med.) The passage of the corpuscular elements of the blood from the blood vessels into the surrounding tissues, without rupture of the walls of the blood vessels.

n. The migration of blood cells (especially leucocytes) through the intact walls of blood vessels into the surrounding tissue

n. passage of blood cells (especially white blood cells) through intact capillary walls and into the surrounding tissue