What term refers to a rabbit's ear that is not carried erect?

The term that describes a rabbit's ear that is not carried erect is "lopped ear." This term specifically refers to ears that hang down either fully or partially, often seen in certain breeds of rabbits, such as the Holland Lop or the English Lop. Lopped ears are a distinct feature that can contribute to the breed's overall appearance and are generally a breed standard for those specific types of rabbits.

In contrast, the other terms do not pertain to ear position; "luster" usually refers to the shine or finish of the rabbit's coat, "measurement" pertains to the size or weight of the rabbit, and "massive" describes a rabbit's overall build or type, particularly in terms of being larger or more robust. Each of these terms highlights characteristics that are unrelated to the positioning of a rabbit's ears.