The Trendlenburg position is a specialized way of positioning a patient, essentially putting the patient in an inclined position with their feet raised above their head by 15-30 degrees.

Although it has several medical uses (some of dubious worth) it's primary use is during surgery of the abdomen and genital/urinary tract as the position of the patient pulls the relevant organs away from the pelvis, making them easier to access.

Trendelenburg position at Wikipedia