loop

Concise Oxford English Dictionary © 2008 Oxford University Press:
loop/luːp/

▶noun

• 1 a shape produced by a curve that bends round and crosses itself.

  ■ a length of thread or similar material forming such a shape, used as a fastening or handle.

  ■ (also loop line) Brit. a length of railway track which is connected at either end to the main line and on to which trains can be diverted.

  ■ (also loop-the-loop) a manoeuvre in which an aircraft describes a vertical circle in the air.

  ■ Skating a manoeuvre describing a loop, made on a single edge.

• 2 a structure, series, or process the end of which is connected to the beginning.

  ■ an endless strip of tape or film allowing continuous repetition.

  ■ a complete circuit for an electric current.

  ■ Computing a programmed sequence of instructions that is repeated until or while a particular condition is satisfied.

▶verb form into a loop or loops; encircle.

■ follow a course that forms a loop or loops.

■ put into or execute a loop of tape, film, or computing instructions.

■ (also loop the loop) (of an aircraft) circle vertically in the air.

– phrases
in (or out of) the loop informal aware (or unaware) of information known to only a privileged few.
throw (or knock) someone for a loop N. Amer. informal surprise or astonish someone.

– origin ME: of unknown origin; cf. Sc. Gaelic lùb ‘loop’.