fan of a single member; solo stan
Idol-fandom slang for supporting only one member of a group, as opposed to 箱推し (supporting the whole group).
See also: 箱推し
I'm a solo stan of that group and not very interested in the other members.
It's not about which is better, being a solo stan or a group stan; it's just a different way of enjoying it.
Compound of 単 (single) and 推し (favorite, from the verb 推す 'to recommend'). A relatively recent idol-fandom term.