3 Answers

What is an Intellectual Disability?

People with an intellectual disability have difficulties with thought processes, learning, communicating, remembering information and using it appropriately, making judgements, and problem solving.

An intellectual handicap is present if the level of intellectual functioning is significantly lower than average and there are limitations in two or more adaptive skills, in the areas of communication, self-care, home living, social skills, community use, self direction, health and safety, leisure and work.

The identification of intellectual functioning is largely based upon the intelligence quotient (IQ) test. Using this test, scores of 90 through to 109 are classified as average. People who score less than 70 may be considered to be handicapped by an intellectual disability depending on how well they function in key areas of everyday life.

An intellectual disability may become apparent early in life or in the case of people with a mild intellectual disability, not be diagnosed until school age or later.

Many people with an intellectual disability also have physical disabilities.

Learning challenged. Basically, someone who does not understand what intellectual disability is. 

Intellectual disability is a broad concept encompassing various intellectual deficits, including mental retardation (MR), deficits too mild to properly qualify as MR, various specific conditions (such as specific learning disability), and problems acquired later in life through acquired brain injuries or neurodegenerative diseases like dementia. Intellectual disabilities may appear at any age.
Intellectual disability is also increasingly being used as a synonym for the term mental retardation as used in standard medical references.[note 1]

I would call it  lack of common sense as a definition.