Transcendental Meditation (TM) refers to a specific form of silent mantra meditation and less commonly to the organizations that constitute the Transcendental Meditation movement. Maharishi Mahesh Yogi created and introduced the TM technique and TM movement in India in the mid-1950s. The Maharishi taught thousands of people during a series of world tours from 1958 to 1965, expressing his teachings in spiritual and religious terms. TM became more popular in the 1960s and 1970s, as the Maharishi shifted to a more technical presentation, and his meditation technique was practiced by celebrities. At this time, he began training TM teachers and created specialized organizations to present TM to specific segments of the population such as business people and students. By the early 2000s, TM had been taught to millions of people; the worldwide TM organization had grown to include educational programs, health products, and related services. The TM technique involves the use of a sound called a mantra, and is practiced for 15–20 minutes twice per day. It is taught by certified teachers through a standard course of instruction, which costs a fee that varies by country. According to the Transcendental Meditation movement, it is a non-religious method for relaxation, stress reduction, and self-development. The technique has been seen as both religious and non-religious; sociologists, scholars, and a New Jersey judge and court are among those who have expressed views on it being religious or non-religious. The United States Court of Appeals upheld the federal ruling that TM was essentially "religious in nature" and therefore could not be taught in public schools. TM is one of the most widely practiced and researched meditation techniques. It is not possible to say whether it has any effect on health as the research, as of 2007, is of poor quality.