Parachute cord (also Para cord or 550 cord) is a lightweight nylon kern mantle rope originally used in the suspension lines of US parachutes during World War II. Once in the field, paratroopers found this cord useful for many other tasks. It is now used as a general purpose utility cord by both military personnel and civilians. This versatile cord was even said to be used by astronauts during STS-82, the eighty-second Space Shuttle mission, to repair the Hubble Space Telescope.
Despite the historic association of Para ropes with airborne units and divisions, virtually all US units have access to the cord. It is used in almost any situation where light cordage is needed. Typical uses include attaching equipment to harnesses, as dummy cords to avoid losing small or important items, tying rucksacks to vehicle racks, securing camouflage nets to trees or vehicles, and so forth. When threaded with beads, Para cord may be used as a pace counter to estimate ground covered by foot. The yarns of the core (commonly referred to as "the guts") can also be removed when finer string is needed, for instance as sewing thread to repair gear, or to be used as fishing line in a survival situation. The nylon sheath is often used alone, the yarn in the core removed, when a thinner or less elastic cord is needed such as when used as a boot lace. Ends of the cord are almost always melted and crimped to prevent fraying. In addition to purely utility functions, Para cord can be used to fashion knotted or braided bracelets, lanyards, belts, and other decorative items.
Para cord comes in all kinds of colors and patterns. Below is a color chart from Atwood.