The dictionary lists a loop-the-loop as a thrill ride that sends its passengers in a complete 360 degree circle. It is more commonly used to describe anything doing the same movement. A plane can loop the loop in the sky when turns in a vertical circle.
It follows the general rule of phrasal verbs that are hyphenated when used as a noun or adjective but separate words when used in verb form.
The word loop comes from the Scottish Gaelic lùb which means to bend.
Other phrases which include loop include throwing someone for a loop, which means to shock or astound someone, and to be in or out of the loop, which means to have or not have a certain knowledge of a matter or topic.
Throwing someone for a loop is mainly found in North America.
Any art fair is a maze of paths that loop the loop, a choir of dissonant voices, but a roadmap will usually be discerned, a theme does emerge. [Spears WMS]
You’ll need to circumnavigate a loop-the-loop and pull off an aerial chip over a ramp. [Timeout London]
Just when they think they’ve got it, he takes them on another loop-the-loop of his imagination. [Washington Post]
Lincoln Beachey in an aeroplane looped the loop four times over the dome of the capitol today while President Wilson watched the performance from a White House window. [Lehigh valley Live]
The language in the poem is sensual, and there are some excellent, evocative images: the dog’s tail looping the loop, the bird flitting from red to red, juice to sweet juice, spinning dancer, the faux amis of warp and woof. [Times Colonist]