An invasive device is a device that, in whole or in part, penetrates inside the body, either through a body orifice or through the surface of the body. Period of use: Short term. In medical terms, intravenous"—or IV, for short—refers to the administration of substances into the body through a vein or veins. INTRA means IN and VENOUS means VEIN. It is commonly referred to as a drip. IV therapy, therefore, works by delivering fluids directly into your veins.