what is a chicken head?

The name "chickenhead" refers to an Andy (Replicant in the film Blade Runner)with below avereage intelligence. "Chickenheads" are isolated from the world. They have limited interactions with humans and androids.

I'm afraid the last answer is incorrect.

In Philip K. Dick's novel 'Do Androids Dream of Electric Sheep?' A 'Chickenhead' also known as a 'special' is a human being whose mental faculties have deteriorated as a result of exposure to radioactive dust and fallout. 'Special' is their official name and 'chickenhead' is derogatory slang used as a casual insult.

The DNA of a 'special' has been altered by the fallout that resulted from a nuclear war known as 'World War Terminus. The radiation has tainted their genes and their intelligence decays. Once deemed a 'special' you are ineligible for emigrating from Earth to new worlds on other planets.

J.S. Isidore is a character in 'Do Androids Dream of Electric Sheep?' He is an example of a 'chickenhead'.

The concept is not present in the film Bladerunner.

An 'Andy' is an android (Replicant in the film Bladerunner) but the term 'chickenhead' does not apply to them.