Meaning of FUNCTIONAL in English
[adjective]Is the central heating functional yet (= is it working as it should do)?(specialized) He's suffering from a functional disorder of the ear (= his ear is not working correctly, although it has not been damaged by a physical injury).(specialized, esp. US) It's time something was done about the number of functional illiterates/the rates of functional illiteracy (= the number of people who are able to live and possibly work in society, but who cannot read and write) in this country.
Cambridge English vocab. Кембриджский английский словарь. 2012