Not expected; unforeseen or unanticipated — describes an event or result that differs from what was predicted or expected.
予期しない結果が出たので、テストケースを見直す必要がある。
An unexpected result appeared, so we need to review the test cases.
システムが予期しないエラーで停止した。
The system stopped due to an unexpected error.
旅行中に予期しない出会いがあって楽しかった。
There were unexpected encounters during the trip, which was fun.
予期しない出来事に備えて、計画を柔軟にしておくべきだ。
You should keep plans flexible to prepare for unexpected events.