Definition of "loop"

loop

/luːp/

noun
plural loops
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.
  Quotations
  In 1908 the line was extended to a station called Wood Lane, which was built on a terminal track loop so that trains could turn round and go back the other way, [...]
  2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, page 119
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.
  Quotations
  And stop all sight-holes, every loop from whence / The eye of Reason may pry in upon us.
  c. 1597 (date written), William Shakespeare, “The First Part of Henry the Fourth, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act IV, scene i]
16. Alternative form of loup (“mass of iron”)
17. (biochemistry) A flexible region in a protein's secondary structure.
verb
third-person singular simple present loops, present participle looping, simple past and past participle looped
1. (transitive) To form something into a loop.
2. (transitive) To fasten or encircle something with a loop.
3. (transitive) To fly an aircraft in a loop.
4. (transitive) To move something in a loop.
5. (transitive) To join electrical components to complete a circuit.
6. (transitive) To duplicate the route of a pipeline.
7. (transitive) To create an error in a computer program so that it runs in an endless loop and the computer freezes up.
8. (intransitive) To form a loop.
9. (intransitive) To move in a loop.
  Quotations
  The outstanding Tom Palmer won a line-out and then charged into the heart of the Welsh defence, scrum-half Ben Youngs moved the ball swiftly right and Cueto's looping pass saw Ashton benefit from a huge overlap to again run in untouched.
  2011 February 4, Gareth Roberts, “Wales 19-26 England”, in BBC‎
10. To place in a loop.
  Quotations
  It found that trains often looped on their journey emit 14% to 20% more NOx and particulates than non-stop services.
  2021 January 13, Richard Clinnick, “Longer freight trains boost efficiency and reduce carbon”, in Rail, page 10