Final answer:
Telangiectasia is a vascular disorder that causes red lines or patterns on the skin due to widened blood vessels.
Step-by-step explanation:
The vascular disorder that appears as threadlike, red lines or patterns on the skin caused by widened blood vessels is called telangiectasia. Telangiectasia occurs when the blood vessels near the skin surface become dilated and visible. This condition often appears as thin, red lines or spider web-like patterns on the skin.