Mental retardation term has been replaced by:
Mental deficiency
Mental lack
Mentally challenged
Intellectual disability
American Psychiatric Association (APA) is responsible for naming, defining, and describing mental disorders. In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM - 5), the APA replaced "Mental retardation" with "Intellectual disability (intellectual developmental disorder)".
Definition and Concepts in Sociology & Psychology