Freud was well known for his theory of psychosexual stages. This theory is a model for human development. Freud was motivated to biologically explain the psychology of humans. The model consists of five stages: oral, anal, phallic, latent, and genital. Each of these phases represents a stage in human development. This model is designed around the concept that humans are driven by the gratification of desire. Fixation, or "stuckness" in any one of these stages represents a stunting of normal development.
Stage One: Oral
The oral stage represents the age range from birth to two years old. In this phase, the mouth is the focal point of pleasure. Infants gnaw on things to interact with them, and breastfeed or drink from a bottle. Those who become fixated in this stage may experience nervous tics around chewing, such as gnawing on the end of a pencil.
Stage Two: Anal
The anal stage represents the ages from two to four years old. In this phase, the anus is the focal point of gratification. During this phase of life, humans learn to control their bowels and their bladders. Fixation in this stage can result in anal retentiveness (Freud's model is the origin of this phrase). One who is anal retentive obsessively holds on to order, such as organization and neatness.
Stage Three: Phallic
The phallic stage represents the ages from four to seven years old. In this phase, the penis or clitoris is the focal point for gratification. In this phase, humans begin to identify with their mother or father and become sexually motivated as individuals. The relationship to the parent of the opposite sex is central to this stage, and fixation in the phallic stage may lead to a fascination with one's mother or father in an Oedipal or Electra complex, respectively.
Stage Four: Latency
The latent stage represents ages seven through puberty. In this stage, individuals focus on repressing, or making latent their earlier desires. Individuals fixated in this phase may be sexually unfulfilled.
Stage Five: Genital
The genital stage represents the adulthood of the individual. In this stage, humans mature sexually and fulfill their desire to procreate. Individuals who are fixated in this stage may be unsuccessful sexually or frigid to sexual partners.
Freud's theory of psychosexual stages is one of many models of human development. Like all models, it can attempt only to generally describe a pattern.