/ˈjufoʊ̯/, /ˈjuːfəʊ̯/, /ˈʌfoʊ̯/, /ˌjuˌɛfˈoʊ/, /ˌjuːɛfˈəʊ/
Initialism of unidentified flying object; (loosely) an alien spacecraft. [from 20th c.]