A Loop

1. A length of thread, line or rope that is doubled over to make an opening.
2. The opening so formed.
3. A shape produced by a curve that bends around and crosses itself.
4. A ring road or beltway.
5. An endless strip of tape or film allowing continuous repetition.
6. A complete circuit for an electric current.
7. (programming) A programmed sequence of instructions that is repeated until or while a particular condition is satisfied.
8. (graph theory) An edge that begins and ends on the same vertex.
9. (topology) A path that starts and ends at the same point.
10. (transport) A bus or rail route, walking route, etc. that starts and ends at the same point.
11. (rail transport) A place at a terminus where trains or trams can turn round and go back the other way without having to reverse; a balloon loop, turning loop, or reversing loop.
12. (algebra) A quasigroup with an identity element.
13. A loop-shaped intrauterine device.
14. An aerobatic maneuver in which an aircraft flies a circular path in a vertical plane.
15. A small, narrow opening; a loophole.
16. Alternative form of loup (mass of iron).
17. (biochemistry) A flexible region in a protein's secondary structure.