droop

Droop is a term used to describe a downward bending, sag, or hanging posture of an object, body part, or system under gravity or load. It can be used as a noun or a verb: to droop means to hang down or sag.

In biology and medicine, droop commonly refers to ptosis, the drooping of the upper eyelid. It can also describe facial droop or sagging soft tissues due to aging, nerve injury, or illness, including post-stroke or Bell’s palsy. Botany and horticulture describe droop in plant parts when water deficit or edema reduces turgor.

In engineering and construction, droop describes the sag of cables, wires, beams, or other flexible structures under load. Cable and power-line design accounts for expected droop to ensure clearance and performance. In aircraft design or maintenance, terms like drooped features or control surfaces may appear in reference to specific configurations, but are context-specific.

In electrical power systems, droop characterizes a natural change in voltage or frequency as load varies. Droop control is used to distribute load among multiple generators or distributed energy resources without requiring centralized communication, by letting voltage or frequency setpoints shift in proportion to load. Voltage droop refers to a deliberate decrease in voltage with increasing current to balance supply among resources.

Across disciplines, the core idea of droop is a downward or sagging tendency caused by weight, load, or changing conditions, from anatomical eyelids to cables, and from plant physiology to electrical control methods.