Vascular describes anything related to the tubes that carry fluids through a living body. In humans and animals, vascular refers to blood vessels: the arteries, veins, and capillaries that form your cardiovascular system, carrying blood to every part of your body. When a doctor checks your vascular health, they're making sure blood flows properly through these vessels.

Plants are vascular too. Most plants have tiny tubes running through their stems and leaves, carrying water up from the roots and food down from the leaves. These vascular plants include trees, flowers, and ferns. The tubes work like microscopic plumbing, keeping the plant alive. Some simple plants like moss don't have these tubes and are called non-vascular plants, which is why moss stays small and close to the ground.

You might hear the word in vascular surgery, where doctors repair damaged blood vessels, or in biology class when learning how redwood trees move water hundreds of feet up their trunks. Whether in your body or in an oak tree, vascular systems solve the same problem: how to transport what's needed from one place to another through a complex living organism.