1The top grade in an evaluation scale — the 優 ('excellent', equivalent to an A) on the 優・良・可・不可 scale used in Japanese universities and the like.
今学期は全科目で優を取った。
I got top marks (優) in every subject this semester.
レポートの評価は優だった。
The report was graded 優 (excellent).
あと一つ優があれば、成績優秀者に選ばれる。
With one more 優, I'd be selected as an honors student.
2Superiority or excellence — being better than others. In modern Japanese it usually appears within somewhat formal compounds such as 優劣 'relative merits (superiority and inferiority)'.
両者の優劣はつけがたい。
It's hard to say which of the two is superior.
製品の優劣は価格だけで決まるものではない。
A product's merits aren't decided by price alone.
3Graceful and refined. A literary/archaic usage; in modern Japanese this sense is hardly used on its own and instead appears in compounds such as 優美 and 優雅.
4(Archaic) skillful or accomplished. Essentially obsolete in modern Japanese, found only in classical texts.