This document discusses surgical drains, including their definition, principles, types, uses, advantages, and removal. Drains are tubes used to drain fluid from surgical sites and prevent collections. They can work via gravity (open), capillary action (semi-open), or suction (closed). Drains are used to drain blood, fluid, bile, or air after procedures involving the chest, abdomen, or bile ducts. They promote healing but also carry infection risks. Drains should be removed once drainage decreases or the targeted issue is resolved.