Oṃ Maṇi Padme Hūṃ: What It Actually Says, and Whose It Is

Whose mantra this is

This is the mantra of Avalokiteshvara, the bodhisattva of compassion, and its textual home is the Kāraṇḍavyūha Sūtra, a Mahayana Buddhist text. It is not a Hindu mantra, not Vedic, and not part of classical yoga. It appears here because it turns up constantly in yoga studios and on malas sold as yoga equipment, usually with a translation that does not hold up.

The grammar problem

The familiar "jewel in the lotus" reading treats maṇi and padme as two separate words in a locative relationship. Buddhist scholars — Donald Lopez's discussion is the best-known — point out that maṇipadme reads most naturally as a single compound in the vocative: an address to one who is jewel-lotus, an epithet of the bodhisattva. On that reading the mantra is a calling, not a picture.

Oṃ and hūṃ are seed syllables with no translation.

If you practise it

It is recited on a mala, often to very large accumulated counts, in the context of Buddhist practice with its own instructions and ethics. If that is your path, learn it from that tradition rather than from a yoga website — including this one.