A varicocele, also called varicose herniation, is a dilatation and multiplication of the pampiniform plexus on the spermatic cord, which develops from the reflux of blood via the testicular vein. On the left picture, one can see ectatic veins in the spermatic cord. On the right picture , representation of the venous reflux by valsalva maneuver.
Source of picture and further information: http://www.urologielehrbuch.de/varikozele.html