Jesses are special harnesses put to a raptor's feet to tether the bird to the glove or a perch. They perform the same function as a dog's collar with a leash. Jesses MUST be on both legs. It is a no-no to attach it to only one leg as this will lead to very serious injuries to the bird. A bird does not feel uncomfortable when wearing suitable jesses.
A jess has two parts: anklet and the strap. It can be either split or solid (traditional-style). The traditional-style solid jess is a single piece of leather that makes up the jess and the anklet, without the possibility to remove the slitted jess. Split jesses are far more popular nowadays. Yoll has split jesses.
I apologise for the poor quality video and the noise. I shot on a camera that does not know how to focus on macro, and has microphones in very uncomfortable places, which are constantly touched by hand, making crackling noises. Still, in the conditions of my home, camera that shoots better than my smartphone is not yet to be found.