1. What does it mean?
최애 (最愛) refers to loving something most. In everyday and fan conversation, it labels a favorite person, member, character, food, or other choice. 'Bias' can fit an idol-fandom context, while 'favorite' usually works elsewhere.
Also written or said as bias
2. The nuance
Although it appears frequently in slang guides, 최애 is not simply a new abbreviation: it is an established Sino-Korean word. Context tells you whether the speaker means a favorite artist, a menu item, or something else.
3. Examples
“이 앨범에서 내 최애 곡은 두 번째 트랙이야.”
My favorite song on this album is the second track.
“여기 오면 항상 최애 메뉴부터 시켜.”
Whenever I come here, I order my favorite dish first.
Sources
National Institute of Korean Language
S-Korean School: Korean language guide
References support the meaning and usage. Example sentences are written for NoCapWiki.