What is the definition or description of: decubitus?

Bed sore: Or any wound caused by pressure. Pressure on skin for many hours without pressure release can cause the tissue to die leading to an open wound.

Lying Down: Decubitus means "lying down" and can refer to patient positioning such as lateral decubitus (laying on ones side.) alternately, it can be used to describe wounds such as bed sores which may be called decubitus ulcers, ie: ulcers from lying down.

Pressure sore.: A decubitus ulcer is a pressure sore, caused by unrelieved pressure-induced ischemic tissue death. Decubiti are most commonly seen in areas of chronic pressure (heels, buttocks, thighs, and even the back of the head) in patients who are immobilized without being turned and repositioned. These are commonly elderly, comatose, or paralyzed individuals who cannot offload pressure or move themselves.