Generally speaking, it is Buddhist meditation; Buddhist meditation texts talk about dhyana (or jhana in Pali; where most of mindfulness sources come from) which

Generally speaking, it is Buddhist meditation; Buddhist meditation texts talk about dhyana (or jhana in Pali; where most of mindfulness sources come from) which is another word for proper concentration. All Buddhist meditation is about entering/achieving dhyana as far as I can tell, although I believe the Chan meditation system puts more emphasis on this. Of course, mindfulness meditation nowadays means many different things, but if you go to the Buddhist sources you will find information about this.