In Medicine, a catheter /ˈkæθɪtər/ is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization. In most uses, a catheter is a thin, flexible tube ("soft" catheter), though in some uses, it is a larger, solid ("hard") catheter. A catheter left inside the body, either temporarily or permanently, may be referred to as an indwelling catheter. A permanently inserted catheter may be referred to as a permcath (originally a trademark).
The ancient Syrians created catheters from reeds. "Katheter - καθετήρ" originally referred to an instrument that was inserted such as a plug. The word "katheter" in turn came from "kathiemai - καθίεμαι" meaning "to sit". The ancient Greeks inserted a hollow metal tube through the urethra into the bladder to empty it and the tube came to be known as a "katheter".