U

Ugly duckling	When reviewing birthmarks, one may find a birthmark that stands out very much from the rest, this birthmark will be described as an ugly duckling. These are often birthmarks with suspicion of malignancy. Should be removed for diagnostics on suspicion.
Ulcus	Wound.
Undermining	When a defect is expanded beneath the skin. Used to close a defect by undermining and loosening connective tissue in-depth, so that the skin edges become more mobile and can be pulled further.