look up any word, like bias:
 
1.
anus, sphincter, ballon knot, leather cheerio.
Robbie pulled a muscle in his neck while trying to watch the anal beads emerge from his brown zero.

OR

Robbie relishes in the staccato of anal beads being ripped from his brown zero.

OR

To celebrate the zero he got on his exam, Robbie lubed up his brown zero before inserting enormous Korean vegetables.
by Total Penetration May 26, 2005
 
2.
Similar to ground zero which is the site directly under the detonation of a nuclear weapon. Brown Zero is the area affected by a fart. Usually limited to a room unless the door was left open and it was really raunchy.
After I ate that big bowl of chili, my fiancee was caught at brown zero when I let one rip.
by computernut October 03, 2009