B5 B6 B7 ???

[EpicA6]

I have a 1999 A6 2.8 Quattro. What are these B5 and B6 numbers that I always see associated with the Audi's? Is it just for the A4's or for all Audi's in general? Are they just associated with the cars engine type? If so, what is mine??? Any info anyone could provide would be greatly appreciated!

[02 A6 2.7T]

These are the chassis model for the car. B5, B6 and B7 are A4's.
B5 A4 = (1995-2001)
B6 A4 = (2002-2005)
B7 A4 = (2005-2008)
The 1998-2004 A6, S6, RS6 and allroad are the "C5" chassis.