a two digit code representing a period of time. Application Filing Date - examples: 01/01/1979-12/31/1986 Series 06; 01/01/1987-12/31/1992 Series 07; 01/01/1993-12/31/1997 Series 08; 01/01/1998-November 2001 Series 09; December 2001-Present Series 10