A face with no make-up; bare-faced (no cosmetics).
今日は疲れてすっぴんでスーパーに行った。
I was tired today so I went to the supermarket without any makeup.
すっぴんで会うのは恥ずかしいと言う友達もいる。
Some friends say they're embarrassed to meet people without makeup.
寝坊して化粧する時間がなかったので、仕方なくすっぴんで出勤した。
I overslept and had no time to put on makeup, so I had to go to work bare-faced.
Sobriety or the plain/unadorned state (older/literary use); being without affectation.
酒の席の後、翌日にはすっぴんで元気に出勤した。
After the drinking party, he went to work sober and cheerful the next day.
In video games: having no class/job or being unassigned (e.g. an RPG character with no class).
このゲームでは、すっぴんは最初のジョブで何の特技も持っていない。
In this game, the 'suppin' starting job has no special skills.
すっぴんキャラを育てると戦略が変わることもある。
Raising a bare (no-job) character can change your strategy.