Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. Its origin is in the Latin word vasculum, meaning little vessel.
The vascular system is a network of blood vessels; arteries, veins and capillaries, that carry blood to organs around the body. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood.
In botany, plants with a dedicated transport system for water and nutrients are called vascular plants. Vascular plants include ferns, gymnosperms and flowering plants. A vascular bundle is part of such a transport system.