An rectum of a female or male which has been expanded to a wide state. This is achieved by anal sex or stimulation with another object or sex toy.
A gaping asshole is created when the anal sphincter is stretched from anal penetration to reveal a 'gaping' effect. This is seen in varieties of hardcore pornography featuring anal sex.
I was having anal sex with her, my penis was so large for her that when I pulled out and saw her gaping asshole.