The Tibetan word for mahamudra is chag gya chenpo (chak chen for short). In Sanskrit,maha means “large” or “great.” It corresponds exactly to the meaning of the Tibetan word chenpo. Mudra, or chag gya, has many meanings. It can refer to the hand gestures used in vajrayana ritual practices; to the symbolic ornaments worn by visualized deities; to the female consort of a deity, who is the aspect of knowledge, inseparable from the masculine quality of skillful means; to a human consort in the practice of karmamudra; or to a seal, such as the stamp or seal of a monarch. Commentators who emphasize the meaning of “seal” will often explain how mahamudra means that the entire world of appearances is sealed or marked by emptiness.
The term chag gya can be further broken down into two components: chag and gya. Chagis the honorific word for hand, the term appropriate when referring to the hand of an elevated person, such as the guru, or to the hand of a deity. When this meaning is highlighted, the shortened term for mahamudra becomes a pun in Tibetan: chak chen, or “big hand.” Gya by itself means a “seal.” Sometimes terma texts are “sealed” for secrecy by repeating this word: gya gya gya.
In the Treasury of Knowledge, Jamgön Kongtrül the Great defines mahamudra as:
Chag gya, or “seal,” refers to union; chenpo, or “great,” refers to this union’s nature fully pervading all the phenomena there are—no phenomenon lies beyond it.
Here, union refers to the unity of appearance-emptiness, awareness-emptiness, or bliss-emptiness. This union is nondual. Two are not joined to become one. Rather, their nature is inseparable, in the same way that water cannot be separated from wetness. As the Heart Sutra might put it, appearance is emptiness; emptiness is appearance. Addingchenpo means that it is so great that it completely transcends concept.