Khecarī mudrā — the seal of the sky-wanderer. It is perhaps the most important technique of classical haṭha yoga. It receives more verses than any other practice in the text.

“Of great secrecy” (mahāguhyam). This technique was not taught to just anyone; it required preparation and maturity. Its power is so great that it must be protected from inappropriate use.

The name means “moving in kha” — space, ether, the void. The tongue becomes a vehicle of spatial transcendence.