Cat "massage" refers to the action that a cat regularly presses/lifts two front paws alternately on a soft object (such as a mat or another hairball). Not all cats use the same massage method. Some meows don't lift their paws at all, and some meows "massage" with four paws. Not all cats can "massage", which is more common among young cats and adult cats.
Four-claw massage
There are many explanations for cat massage. Let's list them one by one.
Innocent, from the beginning of the kitten, the fur ball began to "massage." The mother of the newborn fur ball started her job as a nurse before the Royal Shovel Officer. Kittens in infancy will instinctively press their mothers' breasts to stimulate their mothers' milk production. So why do adult cats have this behavior? Even if pressing the surface of a soft object does not produce milk, this feeling will remind adult cats of their mothers' breasts in infancy, so it can be considered as the "childlike innocence" of adult cats.
Painful love
If you are "loving" the hairball lying on your leg, caress it and make it comfortable, it may also give you "love" feedback. However, this kind of "love" really hurts, because the happier they are, the deeper their claws will be. So before you accept the cat's love, try to put a thick mat on your leg (but then you won't feel the massage of the meow mat). If you don't like the cat's love, don't punish it, because it doesn't know it will hurt you. A compromise is to cut the cat's nails, so that you can feel the massage of the meat pad without being too painful by the claws.
Stretching exercise
Cats are natural yoga masters, and they won't miss any chance to "stretch their fists", even when yawning. Imagine, if you want to yawn, isn't it best to grab the surface of an object? "Massage" may be one of many stretching exercises for cats.