A person with intellectual disability has intellectual functioning which is significantly below average. Together with this, he/she has limitations in adaptive behaviour which affects his/her self-help, living or social skills. It is not an illness or a disease, but a condition, which can occur anytime before, during or after birth (before 18 years of age)

Intellectual disability may occur before birth due to inheritance, chromosomal abnormality or trauma, malnutrition and infection to the mother. It may also occur during birth due to asphyxia leading to brain damage during prolonged labour and trauma. Finally, it can also occur after birth through infections and injury leading to brain damage. This is not an exhaustive list. There are many cases of intellectual disability that have no known causes.

Persons with intellectual disability typically have short attention span and difficulties remembering information. They typically lack the ability to regulate their own behaviour or other people's actions and tend to suffer from delayed language development. Their learning rate is slow and they tend to lack the correct social skills to mix and mingle with others.