In accordance with our prior classification of structures pigmented by melanin, vessels are best described by simple geometric terms that are defined in a lucid fashion. [3] Consequently, we apply the terms dots, clods, and lines also to vessel morphology. Dots are tiny round spots not extending in any direction (no length and no breath), clods are well-circumscribed, solid objects larger than dots that may take any shape (length and breath), and lines are two-dimensional continuous geometric figures extending in one direction (only length but no breath). Vessels appearing as lines (linear vessels) may take different forms: Linear vessels without a bend are straight. Linear vessels with only one bend are looped if the bend is sharp (180°) and results in a reversal of direction (U-turn) and curved if the bend is gentle. Linear vessels with more than one bend are termed serpentine if the bends are arranged in a snakelike fashion, helical if the bends are twisted along a central axis, and coiled if the bends are convoluted compactly (Fig. 1). The additional attributes thin and thick and short and long may be applied to all types of linear vessels. The attribute thick should only be applied if the thickness of the vessels exceeds the diameter of normal nail fold capillaries by far. The attribute long may be used for straight, serpentine or helical vessels if they cross a significant part of the lesion.