I've been getting back into doing yoga after a long, long (long) break. I noticed that on many of the instruction videos I've seen, there isn't much teaching on what to do with your mind while you are in a certain pose. And they don't spend much time in any one pose; nothing longer than what it takes to get through understanding the mechanics.
Something I have found in just practicing is that the mind is part of doing the pose. Where there is tension, you massage it with the mind so that it can release. When the mind is separate from the body, the body tends to seize up as it attempts to match the ideal form in the mind.
Perhaps we could say that the ego is this tension, stress in its most common form. That might be a good definition because we all know what stress is and techniques to remove it. When I think about anyone whom I would consider ego-less, they are completely free of stress. They aren't worried about anything, they don't think they should be doing something besides what they are doing and they aren't starting any drama with anyone.