A loop is a roundish, coiled shape, like the shape a piece of string or rope makes when it crosses itself. To start knitting, you need to put a loop of yarn on the end of one of your needles.
Loops are ovals or circles and are often made from rope or other fibers, like the loop at the end of a cowboy's lasso. The verb loop means to form the shape of a loop in the sky; or to make a loop from string or some other material. If something "throws you for a loop," it catches you by surprise, and if you're "in the loop," you have access to information that others might not have.