Altricial  -  The term "altricial" refers to species in which infants are born unable to fend for themselves. It is contrasted with "precocial," which refers to species, such as horses and other hoofed animals, in which the newborn is immediately able to find food, run from predators, etc.

Autism  -  A developmental disorder characterized by mental retardation, impairments in language, changes in sensory function, repetitive or ritualized motions, and marked deficits in theory of mind.

Accommodation  -  Accommodation is a process of changing one's representation of the world to fit the existing evidence. According to Piaget, it is one of the two "functional invariants" that drive development.

Assimilation  -  Assimilation is the process of changing one's interpretation of the world to fit one's representation of it. According to Piaget, it is one of the two "functional invariants" that drive development.

Concrete-Operational Stage  -  The concrete-operational stage is one of the four stages in Piaget's developmental theory. It lasts from ages seven to eleven and is characterized by an ability to mentally manipulate representations of real-world ("concrete") objects.

Formal-Operational Stage  -  The formal-operational stage is one of the four stages in Piaget's developmental theory. It starts around age eleven and lasts through adulthood. It is characterized by an ability to mentally manipulate symbols, such as mathematical equations or linguistic sentences, that are not connected to real-world objects.

Metacognition  -  Thinking about one's own thought processes.

Object Permanence  -  Object permanence is the concept that objects continue to exist even when they cannot be seen. The acknowledgment of object permanence starts, according to Piaget, during the preoperational stage.

Preoperational Stage  -  The preoperational stage is one of the four stages in Piaget's developmental theory. This stage lasts from ages two to seven. It is characterized by a growing ability to verbalize and symbolize concrete objects, but an inability to perform "operations"--mental manipulations or logical transformations--on them.

Sensorimotor Stage  -  The sensorimotor stage is one of the four stages in Piaget's developmental theory. It lasts from birth to age two. It is characterized by the development of internalized representations of concrete objects that grow out of the child's perceptions of and actions on those objects.

Visual Acuity  -  Visual acuity refers to the "spatial resolution" of a person's vision: a person with high visual acuity can distinguish between narrower stripes of different intensities than a person with low visual acuity.