When a woman stand on her head/hands with legs spread, balancing as she shakes her ass front to back. This motion has been made popular by several porn movies and the song "Pussy Poppin'" By Luda.
When you fuck a virgin for the first time in her pussy pops all I know is I fucked three versions and all three of them their pussy popped one girl said she was a virgin but her pussy didn't pop and after interrogating her I found out she had been with four other guys