Intellectual disability (ID), also known as general learning disability and mental retardation (MR), is a generalized neurodevelopmental disorder characterized by significantly impaired intellectual and adaptive functioning. It is defined by an IQ under 70 in addition to deficits in two or more adaptive behaviors that affect every day, general living.

Intellectual disability is subdivided into:

• syndromic intellectual disability: in which intellectual deficits associated with other medical and behavioral signs and symptoms are present.Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.
• Non-syndromic intellectual disability: in which intellectual deficits appear without other abnormalities. Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.

Intellectual disability (ID) begins during childhood and involves deficits in mental abilities, social skills, and core activities of daily living (ADLs) when compared to same-aged peers. There often are no physical signs of mild forms of ID, although there may be characteristic physical traits when it is associated with a genetic disorder (e.g., Down syndrome).

The level of impairment ranges in severity for each person. Some of the early signs can include:

Delays in reaching or failure to achieve milestones in motor skills development (sitting, crawling, walking)

Slowness learning to talk or continued difficulties with speech and language skills after starting to talk

Difficulty with self-help and self-care skills (e.g., getting dressed, washing, and feeding themselves)

Poor planning or problem solving abilities

Behavioral and social problems

Failure to grow intellectually or continued infant-like behavior

Problems keeping up in school

Failure to adapt or adjust to new situations

Difficulty understanding and following social rules