Damaru

Skt., damaru; double drum
Tib., thod rnga, gcod rnga; double skull drum

When encountering the term damaru within an Indian context, it refers to a double-headed drum usually made from wood and looking like two halves of a coconut have been joined back to back. A damaru may have one or two strings attached with a small ball or bead that make a rattle-like sound when the drum is rotated. This type of drum is often carried by Shiva and/or his various manifestations and symbolizes speech and/or language (as a form of sound) and, in extension, the sacred alphabet by means of which sound creation proceeded on its way.

Although the term damaru is often used in a Tantric context as well, especially in Tibet, it should be tranlated as thod rnga only if the drum is made from human skull bone; considering that thod means skull.
This form of damaru, made from the crowns of two human skulls, always has the said strings and beads attached; and its usage make it more into a rattle than a drum. Carrying this object identifies a given deity, mainly the Dharmapalas (Skt., protectors of the teachings), as being tantric in nature.

When carried by a human adept, the double skull drum (thod rnga) usually identifies her or him as a Chöd-pa, i.e. a practitioner of Chöd, whence the other name for those drums: gcod rnga.