Id, ego and super-ego are the three parts of the psychic apparatus defined in Sigmund Freud's structural model of the psyche. According to this model, the Id is the set of uncoordinated instinctual trends, the ego is the organized, realistic part, and the super-ego plays the critical and moralizing role. While super-ego can stop you from doing certain things that your Id may want you to do, the Ego performs a balancing act between these two parts of the psyche, in order to cope with reality.
The Id is the unorganized part of the personality containing the human's instinct drives. The Id contains the libido, as a primary source of strength, being unresponsive to the demands of reality. The Id acts according to the "pleasure principle", seeking to avoid pain or unpleasure with no organization, a complete lack of an idea of time, and the need of immediate satisfaction.