Reference to the anus in regards to the performance of Anal Sex.
1. I played the back nine with my girlfriend last night.
2. I teed off on the back nine but she kicked me off the course.

by Wes Wylerson April 20, 2006
Get a back nine mug for your coworker Helena.
The backside of a female.
Bro, did you see the that girl that just went by.

Hell yes, that lady had a fine back nine.
by sanfred January 18, 2011
Get a Back Nine mug for your cat Julia.
When you get little sleep at a friend's house/wherever you passed out, head home, and get the rest of the sleep you need to get a full night's rest; a non-contingent nine hours of sleep.
John: Wow, three hours of sleep at this party? I had better head home to get the back-nine.
by kingPontus January 24, 2010
Get a Back-nine mug for your mate Zora.