BMWs have always had platform designations to refer to a specific platform. Obviously, numbers only increase and BMW is on the verge of moving to another letter, the Fxx platforms

For example:

E36: 3-series, 1993 (?)-1999
E38: 7-series 1994-2001
E39: 5-series 1996-2003
E53: X5 1999-2006
E60: 5-series 2004-present
E65: 7-series 2002-2009
E83: X3 2004-present
E85: Z4
E87: 1-series 2004-present