na-adjective, noun
poor result; bad record; failure
Refers to an unsatisfactory outcome or performance, often in academic, professional, or competitive contexts. Can be used as a noun or adjectival noun.
今回の試験は不成績に終わった。
This exam ended with a poor result.
彼の不成績な態度が問題だ。
His poor performance attitude is a problem.
失敗 is a more common word for 'failure' in general, whereas 不成績 is more formal and often used in written or evaluative contexts.
Compound of 不 (fu, 'not') and 成績 (seiseki, 'results'), literally meaning 'not good results'. The exact historical derivation is uncertain, but the word follows a common pattern of negating a noun with 不.