The ego is a concept in psychology that refers to the part of the mind that mediates between the conscious and unconscious mind. It is responsible for reality testing and decision making. In terms of development, the ego is one of the three components of Sigmund Freud's psychoanalytic theory of personality, along with the id and superego.
The ego stage of development occurs during early childhood, around the age of 2-3 years old, according to Freud's theory. During this stage, children begin to develop a sense of self and learn to differentiate themselves from others. They also start to understand cause and effect relationships and develop basic problem-solving skills.
Overall, the ego stage of development is crucial for the formation of a healthy sense of self and the ability to navigate the world effectively.