Over-Gape is when the inside walls of the rectum are forcefully expanded to such an extent (through penetration of course!) that it will not expand any more without ripping the soft tissue of the anus. Over-Gape will resemble that of a deep chasm or bottomless pit. A fist would fit inside without touching any side.
I Over-Gaped Jenny so bad last night that she didnt even feel herself have a bowel movement!