A phrase used to denote that a couple of men, who are both in relationships, are free to act like men and otherwise play and engage in general stupidity.
Taken originally from a skit on the comedy show 'The Kids in the Hall' in which the wives of a pair of married men leave on a short vacation. The two married men are now able to party and generally act foolish, exclaiming, "The wives are gone, we have the whole country to ourselves!" before embarking on an, apparently, nationwide party.
Currently, the term is used on any occasion when a small group of men (not less than two, not more than five) are allowed to generally have a good time because their wives are otherwise engaged.

Note: Often accompanied by an impromptu victory dance, during the saying of, 'Whole country to ourselves!'