A maebari is a small (usually rectangular) piece of cloth or covering that goes over the vagina and ass hole. This small cloth completely covers the lower female private parts while giving the bare minimum of coverage necessary to be decent. This is usually not worn with panties or a thong.
This word comes from Japanese for 前(mae) for "front" and 張り(bari) for "object that is pasted on." Its use is mainly in Japan.
Satoko was soo teasing us with her maebari. It was like you could see her pussy lips, but not quite.