"The space of Aham is where kechari mudra (free movement in the space of the heart) is realised. Kechari mudra is considered the supreme state of spiritual evolution."
It's not talking about the physical mudra some of us do with our tongue, btw - true khechari -- true "moving in the sky" -- is referring to enlightenment.
Aham is the Sanskrit term for "I" - and is an essential mantra of Kashmir Shaivism//Trika Shaivism.