According to MedlinePlus, "IV" stands for "intravenous," which means "within a vein." The term "IV" typically refers to an intravenous needle or tube used to deliver additional blood, medication or other fluids directly into the body's bloodstream.
Healthline notes that IVs are used to deliver medicine when the drug cannot be taken orally, when it needs to be absorbed into the body immediately or when it needs to be given at a steady rate over time. IVs are commonly used to give saline or other fluids to a patient who is dehydrated. A doctor or nurse administers an IV by finding an appropriate vein and inserting a needle or tube into the vein.