Vena comitans is Latin for accompanying vein. It refers to a vein that is usually paired, with both veins lying on the sides of an artery. Because they are generally found in pairs, they are often referred to by their plural form: venae comitantes.
Venae comitantes are usually found with certain smaller arteries, especially those in the extremities. Larger arteries, on the other hand, generally do not have venae comitantes. They usually have a single, similarly sized vein which is not as intimately associated with the artery.
Examples of arteries and their venae comitantes:
Examples of arteries that do NOT have venae comitantes (i.e. those that have "regular" veins):