A disease. They occasionally can be a symptom of something else but most often they are a disease state themselves.
Vascular disease/PAD. Hard arteries with plaque is atherosclerosis. Other diseases accelerate pad plaque build up; hypertension, hyperlipidemia, diabetes, and nicotine addiction. Heart attack, stroke, limb loss, sudden death are vascular events. Medical therapy for all the diseases is important. Surgical therapies, stent, balloon and bypass when plaques cause symptoms.