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2.
A reducing number of men in an area/school/community.
Carol: I need a date to the prom
Jessica: Good luck, we're in such a mancession.
by michaliann October 01, 2009
 
1.
Term used by economists to reflect that for the first time in economic history, the male unemployment rate has surpassed the female unemployment rate. In the last year (2008-09) 82 percent of pink slips have been handed to male workers.
Denise: "What's the deal with all of the stay-at-home dads on your block?"

Bev: "It's not by choice, they are all victims of the mancession."
by windowofopportunity June 22, 2009
 
3.
A period of temporary or extended romantic decline during which dating, relationships and intimate encounters are reduced or completely absent from a woman's life, generally identified by a lack of qualified men in close geographic proximity in two successive quarters
Men were plentiful in undergrad; however, when I've been in the midst of a mancession since graduation.
by aj2fab January 10, 2012