na-adjective, noun
Literary or formal adjective/noun describing something as beautiful, excellent, or favorable. Often used in written language, names, or set phrases rather than everyday speech.
この作品は佳と評価された。
This work was evaluated as excellent.
成績表には佳の評価が付いていた。
The report card had a grade of "ka" (good).
美しい is the standard word for 'beautiful' in both spoken and written Japanese; 佳 is more limited to formal or classical contexts.
The kanji 佳 is composed of 亻 (person) and 圭 (a mound of earth), originally suggesting a person of fine appearance. The reading か is the on'yomi. The exact historical derivation is uncertain, but the character has long been associated with beauty and excellence.