Ego integrity vs. despair is a key concept in Erik Erikson's theory of psychosocial development, which describes the final stage of an individual's life cycle. Ego integrity refers to the sense of acceptance and satisfaction with one's life, while despair represents the feeling of regret, bitterness, and fear of death. This term is closely connected to the individual's ability to reflect on their life and find meaning in their experiences as they approach the end of their lifespan.