means A curve or line that bends around and rejoins itself, or by extension a repeating cycle that returns to where it started.

from English from the late Middle Ages, first describing a loop of rope or thread — the doubled-over bend you could pass something through. Its deeper roots are murky; it may be related to a Celtic word (compare Irish 'lúb,' meaning a loop or bend), though the connection is uncertain. The looping sense of 'going round and round' and the computing 'loop' came much later, each borrowing the same simple image of a line that bites its own tail.