What is the meaning of Retarded?

Delayed; delayed in development, hindered; impeded.

Having mental retardation; mentally deficient or underdeveloped.

Specifically, having an IQ below 70.

Extremely stupid; obtuse

Designating a parameter of an electromagnetic field which is adjusted to account for the finite speed of radiation.

simple past and past participle of retard

retarded; having mental retardation; mentally deficient

a retard

Source: wiktionary.org