Om Namah Shivaya (Devanagari: ॐ नमः शिवाय; IAST: Oṃ Namaḥ Śivāya) is among the most widely recited Hindu mantras and is regarded as the foremost mantra within the Shaivite tradition. The phrase Namah Shivaya is generally rendered as "salutations to the auspicious one" or "adoration to Lord Shiva".
The mantra is known as Shiva Panchakshara, or simply Panchakshara, meaning the "five-syllable" mantra, referring to the syllables Na, Ma, Śi, Vā and Ya, which are counted excluding the syllable Oṁ. The mantra is dedicated to Shiva and occupies a central place in Shaiva devotional practice and liturgy.
The five syllables appear in the Shri Rudram Chamakam, a hymn forming part of the Krishna Yajurveda, and also in the Rudrashtadhyayi, which belongs to the Shukla Yajurveda. These Vedic sources have contributed to the mantra's enduring liturgical and devotional importance across various schools of Hindu worship.
According to traditional usage, the five-syllabled form of the mantra (without Oṁ) is held to be open to recitation by all persons, including those classed as śūdras and cāṇḍalas. The six-syllabled form, which prefixes Oṁ, is traditionally restricted to dvijas (the "twice-born"). This distinction is reflected in classical texts that prescribe rules governing the chanting of Vedic and tantric mantras.
Adapted from the English Wikipedia article on Om Namah Shivaya.