Meaning of “unbelievable” - Learner’s Dictionary

unbelievable

adjective uk us /ˌʌnbɪˈliːvəbl/
EXTREME

B1 extremely bad or good and making you feel surprised:

It's unbelievable how lucky she's been.
NOT LIKELY

B2 not probable and difficult to believe

unbelievably adverb

(Definition of “unbelievable” from the Cambridge Learner’s Dictionary © Cambridge University Press)