vertical stain
The frontal secretions left on a woman's pair of panties. A womans genital moistness on her panties. When the vagina releases it's juices onto a pair of panties and leaves a stain, a vertical stain.
My panties will have a vertical stain by the end of the day. I saw her vertical stain on her panties. He got me so wet, my panties now have a vertical stain on them.