Fixation refers to arrested development at a particular stage of psychosexual development attributable to excessive or inadequate gratification at that stage.
Other /More definition:
Fixation is defined as a lasting conflict developed as a result of frustration or over-indulgence; the tendency to repeat wrong solutions or faulty responses, especially as a result of becoming blind to alternatives. It is the defense mechanism that occurs when the frustration and anxiety of the next psychosexual stage cause the individual to be arrested at his or her current level of psychosexual development; the tying up of psychic energy at a particular psychosexual stage, resulting in adult behaviors characteristic of the stage.
Moreover, it refers to:
(1) arrested development at a particular stage of psychosexual development attributable to excessive or inadequate gratification at that stage. According to Freud, it is arrested development at a particular psychosexual stage, usually occurring as a means of coping with existing conflicts and preventing movement to the next stage, where stress may be even greater;.
(2) the attachment of sexual energy to a given stage of development within Freudian theory.
In Freud's theory, Fixation is the failure to move forward from one stage to another as expected. In the study od Sensation and Perception, Fixation is defined as the pause of the eye that occurs between eye movements as a person scans a scene. It is the time spent focused at a given location during reading the time between eye movements.
List of books: Fixation