What is really 'ego death'?

I've tripped a few times, my highest dosage being 400ug LSD and another time 60mg 4-aco-dmt. I never really understood the term ego death. I've had experiences where I feel I was nothing but pure energy shooting around in the universe. But what is ego death, and what is the ego? How can it die? I mean I'm always conscious while tripping, so I don't understand how one's ego can die.