[Smokeyblue]

http://www.senate.gov/reference/glossary_term/class.htm

class - Article I, section 3 of the Constitution requires the Senate to be divided into three classes for purposes of elections. Senators are elected to six-year terms, and every two years the members of one class—approximately one-third of the senators—face election or reelection. Terms for senators in Class I expire in 2019, Class II in 2015, and Class III in 2017.

[lonevoice]

Thank you! I love it when I learn something new.