I've carried this definition around probably since 1984 when I first heard it from New Testament scholar Dr. Marcus J. Borg (author of many books and former Jesus Seminar member). It seems pithy and descriptive, so I duplicate it "in so many words", namely: Religions and spiritual systems tend to define the ego as the anxious, grasping self.
For me, this definition is handy and pragmatic for the personal reason that, with Freud, I view the ego - my little flickering ego-flame - as "the seat of anxiety". On a less personal level, the definition can apply across a wide range of personality descriptors without getting hung up in - say - materialistic/neurological definitions of ego, or in any particular psychological school's definition.
It seems that fruitful spirituality does indeed positively impact the anxious, grasping self, whether from the stereotypical Western view of "the freeing up of the self"; or from the familiar Eastern/mystical view of "freedom from
the self". Most of us are familiar with Buddhism's methods for loosening up "the ego" and/or transcending it; and the Gospel Jesus encourages us to take up our cross (Luke: "daily") on a path of ego-diminishment; Paul view baptism as a participatory way of "dying and rising with Christ"; Ramana Maharshi taught turning away from the ego to constant remembrance of the Self; etc., etc.
To me, the more Dharma and the more "Spirit" and the more Awareness and the more "God" ... lead to a less grasping, anxious self, and to less ego attachment in general.
Obviously, I'm not being very profound, but I just wanted to share this particular definition of ego for those who haven't heard of it, and for those who might find it as handy as I do