desconocido

listen to the pronunciation of desconocido
Spanish - English
someone or something that is unfamiliar
confidential
fameless
unbeknown
newcomer
unknown

Although most islands in the ocean have been mapped, the ocean floor is generally unknown. - Aunque la mayoría de las islas en el océano han sido mapeadas, el suelo oceánico es por lo general desconocido.

The symbol X usually stands for an unknown quantity in mathematics. - La letra x en matemáticas usualmente representa un valor desconocido.

unknown, someone or something which is not known
undiscovered
unknown person
complete stranger