Cupping

First the doctor produced from his black bag a dozen small glasses like wine glasses, then the student burned a match inside each glass to exhaust the air, then the glass was popped on to the man's back or chest and the vacuum drew up a huge yellow blister. Only after some moments did I realize what they were doing to him. It was something called cupping, a treatment which you can read about in old medical text-books but which till then I had vaguely thought of as one of those things they do to horses. Cupping is a pre-modern "medical" practice, consisting of sticking cups to the victim patient's skin via suction with the idea to make them better. Documentary evidence exists that the practice was widespread in Egypt as far back as 1550 BCE. The ancient Greeks also practiced cupping; Hippocrates was credited with using the practice in 400 BCE. As no ancient medical treatment is stale enough for alternative medicine fans, it is still practised (in Unani, traditional Chinese medicine, and Ayurveda, among other things), commonly under the guise of "detoxification". There is absolutely no evidence that cupping has any positive effect on one's health and may actually be harmful, with the possibility of blood vessels rupturing from the pressure and burns if fire is used. It also has the possible side effect of making the patient look like a moron.

Cupping technique
The cups are usually applied to the back. The suction is usually achieved via heating the cup before applying it to the skin. After the air inside cools down, it "shrinks" and creates negative pressure, drawing skin in and making the cup stick to it.

Depending on the suction force and the skin of the patient, cupping may leave characteristic circular bruises that will last for some time after the procedure.

"Cupping" usually refers to sucking cups only, but there's also "wet cupping", when the skin is punctured before a cup is applied. The negative pressure draws blood (and supposedly, toxins), thus combining cupping with bloodletting, another ancient medical practice.

As the page quote demonstrates, there is a description of cupping in a Paris hospital in George Orwell's essay How The Poor Die, where he was surprised to find it practised.

Cupping is popular with some sportspeople and made headlines during the 2016 Rio Olympic Games when US swimmer Michael Phelps and other Olympic athletes appeared looking like he just lost a fight to an octopus with the distinctive circular bruises on their bodies.

Non-woo use
Besides their use in alternative medicine, the cups are sometimes used as sex toys in certain BDSM practices.