A "lackwit" in Westeros refers to a person who is lacking intelligence. They are also often called "simpletons", "simple-minded", or sometimes just "simple". They are frowned upon by society. There are lackwits in all strata of society. Despite being lackwit some highborn can still inherit; for example, Lollys Stokeworth, who becomes the Lady of Stokeworth after the deaths of her mother Tanda Stokeworth, and her sister Falyse Stokeworth. Men have been known to marry lackwit heiresses. Male lackwits sometimes become fools.
Uncertainty about Moon Boy
On occasion, Moon Boy is described as a simpleton or lackwit. However, on multiple occasions, several characters wonder whether or not Moon Boy is truly a lackwit. Moon Boy is known to mock people with deft cruelty, which puts doubts on whether or not he's truly a simpleton. On one occasion, a drunken Dontos Hollard accuses Moon Boy of being a spy of Varys and that his simple-mindedness is just an act.