adverb, noun which may take the genitive case particle 'no'
more than expected; beyond expectations
Used adverbially or with の to describe a result that exceeds what was anticipated. Often appears with verbs like なる, だ, or 難しい.
試験は予想以上に難しかった。
The exam was more difficult than expected.
予想以上の成果が出た。
We achieved results beyond expectations.
予想外 means 'unexpected' or 'contrary to expectations', often with a nuance of surprise or something unforeseen. 予想以上 is more neutral and simply indicates exceeding a predicted level.
Compound of 予想 (expectation) + 以上 (more than, above). The meaning is transparent from its parts.