Intellectual disability (ID), once called mental retardation, is characterized by below-average intelligence or mental ability and a lack of skills necessary for day-to-day living. People with intellectual disabilities can and do learn new skills, but they learn them more slowly.

There are varying degrees of intellectual disability, from mild to profound. The term "mental retardation" is no longer used, as it's offensive and has a negative tone.

Someone with intellectual disability has limitations in two areas. These areas are:

Intellectual functioning. Also known as IQ, this refers to a person’s ability to learn, reason, make decisions, and solve problems.
Adaptive behaviors. These are skills necessary for day-to-day life, such as being able to communicate effectively, interact with others, and take care of oneself.

IQ (intelligence quotient) is measured by an IQ test. The average IQ is 100, with the majority of people scoring between 85 and 115. A person is considered intellectually disabled if they have an IQ of less than 70 to 75.