A nice, tight little ass on a male or female (depending upon your preference) that is primed and aching for attention, arched up in the air and ready for exploriation and penetration. Alternatively, for non-beef fans, Bone In Ham is a Slang Substitute
Roger: How as your day yesterday?
Carl: Long day at the office but a sweet surprise when I got home.
Roger: How so?
Carl: Walked in the door and Tonya was in the middle of the room sporting a Bone In Filet.
Roger: And?
Carl: I split dat ass! She thought I was Torting her. But as always, I gave her a Butler's Wipe.
A bone in occurs during intercourse between a male and a female, when the female has exercised her vaginal muscles to the extent that she is able to force her labia through the base of the male's crotch, absorbing a large portion of his pelvic region.
It can also occur during sex between two males, where the receiving male has exercised his anus enough to perform the act.
Scholars are still unsure whether this came before or after the bone out.