In hip hop, it refers to a 16 bar verse, which is the average size verse in a rap song. "Bar" is a musical term, sometimes called a "measure", indicating a section with a defined amount of beats in it.
Yo dawg! I'm finna drop these sixteens right about now, get that mic ready!
Good purple weed with a grapey, fruity pebblish taste i.e GrandDaddyPurple, Purple Urkle, Purple Kush or Mendo Purps. Popular in NorCal, highly sought after everywhere else.