Which term is used to describe the structure known as the ischium?

The term "isch/o" is the correct choice for describing the ischium. In medical terminology, "isch/o" specifically refers to the ischium, which is one of the three main bones that make up the pelvis. This root is derived from the Greek word "ischion," which means hip or hip joint, highlighting its association with the pelvic area.

The other terms provided do not relate to the ischium. "Kerat/o" pertains to the cornea or horns, often used in discussions regarding eye anatomy or conditions affecting the cornea. "Kal/i" refers to potassium, a mineral that is crucial for various bodily functions, including nerve transmission and muscle contraction. "Irid/o" is associated with the iris, which is the colored part of the eye that helps control the amount of light that enters the eye. Understanding these distinctions helps in grasping the broader context of medical terminology and its specific applications in anatomy and physiology.