Intravenous therapy (IV therapy or iv therapy in short) is the infusion of liquid substances directly into a vein. Intravenous simply means "within vein". Therapies administered intravenously are often included in the designation of specialty drugs. Intravenous infusions are commonly referred to as drips because many systems of administration employ a drip chamber, which prevents air from entering the blood stream (air embolism), and allows an estimation of flow rate.