In typical usage, retard is a pejorative term either for someone with an actual mental disability, or for someone who is considered stupid, slow to understand, or ineffective in some way as a comparison to stereotypical traits perceived in those with mental disabilities.
The English language, along with other European ones, adopted the word and used it as similar meaning, slow and delayed.
[11] Much like today's socially acceptable terms idiot and moron, which are also defined as some sort of mental disability, when the term retard is being used in its pejorative form, it is usually not being directed at people with mental disabilities.
She worked with her parents to have the words "mentally retarded" officially removed from health and education code in Maryland, her home state.
[13] The goal of this change in phrasing was to remove language that may be considered derogatory to communities.