Maybe the briefest definition of “ego” is a belief in the thought I.
There is an idea of “I” as a segment of what is (my human self, a part of my human self, pure awareness, etc), a belief in this idea (making it appear real), and this belief create the whole I-Other dynamic we are so familiar with.
So the ego is merely a belief in an idea – ephemeral and tenous in its nature – which creates all sorts of consequences experienced as very real, including a sense of separation, blind attractions and aversions, and so on.
Our human self is quite different. It is the temporary and local manifestation of the world of phenomena, a vortex in a stream, a flow of matter and energy in a temporary pattern which itself is fluid. Our human self is there with or without the ego – the belief in the idea of I.