Inner Body meditation
Eckhart Tolle calls it "inner body". In Vipassana, Goenka calls it "Free Flow" or "Bangha" (sometimes spelled Bhanga or Banga). Some say that it is actually the astral body or our energetic body beyond form. They all say that it is a good bridge to go from form to formless and to the absolute.
All these names refer to a subtle feeling of a body vibration, to a sensing of a body frequency. When your mind is sharp, you can feel it very strongly, as if all your body is shaking.
How to sense it? Tolle suggests to try to feel the body from within, Goenka advices to scan the body for regular gross sensations (like pain, tickling, itching, etc.) and suggests that with practice, the gross sensations will turn subtler and subtler until all the body is felt as one field of energy to be scanned in a free flow fashion.
I must say that I found the sensing of this energetic body very powerful both in Vipassana and while reading Tolle's "Power of Now". It connected me with something beyond the mind and triggered experiences and changes that I cannot yet describe.
I will appreciate if others can share their experiences with this "inner body" and references, if exist, to the same thing in other techniques and traditions (I heard there is some similar yogi stuff).