Ham is the seed syllable (bija mantra) of vishuddha, the throat chakra, in the chakra system of tantric and hatha yoga. Each principal centre in the scheme has a governing element, a lotus of a set number of petals, and a seed sound for meditation; vishuddha, the pure one, is assigned to the element ether or space and to a sixteen-petalled lotus, and Ham is the sound by which the meditator focuses upon and is held to activate it. The centre is associated in the tradition with speech, sound and communication, an apt link for the throat, and its element, the subtle space or ether from which sound arises, is the most refined of the five. Like the other seed syllables, Ham is used as pure sound rather than as a meaningful word, in inward recitation and visualisation, and its assignment belongs to the medieval tantric system preserved in the later yoga texts.
Ham is identified in the same tantric physiological scheme, the Shatchakra Nirupana as transmitted through Sir John Woodroffe's The Serpent Power (1919), as the bija, or seed syllable, of the Vishuddha chakra, the throat centre, traditionally visualised as a sixteen-petalled lotus and associated with the ether or space element and with speech, truthful communication and purification. In the scheme's ascending sequence of seed syllables, Lam for the root centre, Vam for the sacral, Ram for the navel, Yam for the heart and Ham for the throat, the pattern typically continues upward to Om at the brow centre (Ajna), with the crown centre (Sahasrara) traditionally held to correspond to no fixed syllable but to silence itself.