A grey hole is an object from which matter and radiation escape, rise to a certain distance above the event horizon, and then fall back in. Compare to a black hole and a white hole
In the case of White Holes, Black Holes, and of Grey Holes, they all have two singularities, one in the past and one in the future.
This is a phrase used when saying that married women sleep around with other males that she is not married to. Just because a woman is married (and has a ring), doesn't mean she doesn't want her hole plugged by someone else.
Friend: Hey, that girl is really cute, but she's married so I can't mess with her.
You: Hey, a ring doesn't plug a hole. Go for it.