Shmuel asked if a certain online Hebrew meditation site was alright. I looked at its brief opening paragraph and saw that the word Buddhism was used at least three times. I told Shmuel that obviously, it is not a place for Jews to learn how to meditate. He then asked; "Is Buddhism idolatry?"
Originally, Buddhism was intended to be a philosophy, a way of life. Then, as it spread, each Asian country that adopted it did not replace its ancient religion, but mixed the new ideas of Buddhism with their old idolatries. This is why each Asian country has a different form of Buddhism today.
Virtually all Buddhist sects teach that there are many different deities. Although a non Jew is allowed to believe that Hashem shared His power with "partners," such as a moon or a constellation, no one is allowed to worship any of those "partners."
The most well-known Buddhist teacher in the world today is the Tibetan dali llama. He once wrote in National Geographic magazine about how wonderful his village deity was. Many years ago he hosted a religious service at his brother's ashram in America. Some 50,000 guests paid to watch him do the three day service. He made a Kalacharkra Mandala which is a Tibetan Buddhist tradition that involves the creation and destruction of a mandala made from colored sand. These mandalas contain 722 deities portrayed within the complex painting.
He then poured the paining into a body of water in order to "bring peace to the World by appeasing the god with four heads and twenty-one arms." This is service to a deity. It is idolatry.
Jews who want to learn how to meditate should learn Jewish meditation and not the meditation practices of other religions. Invariably their spiritual teachings will be embedded within their meditation practices.