A May-December relationship is one where one of the individuals is significantly older than his o her partner. October-October comes from a discussion between House and Cuddy. A man had basically poisoned his two children because he was trying to live up to his younger girlfriend's "expectations." When Cuddy questioned the whole May-December romance, House told her that for that couple it was más like "May-October," implying that the man was middle-aged instead of being much older than his twenty-something girlfriend. Cuddy's response of "Why can't it be October-October?" refers to two middle-aged individuals starting a relationship (aka House and Cuddy). This scene takes place in the season 3 episode "Act Your Age"