Judaism and Christianity considered as a common social tradition in Western culture. Characterized by patriarchy, hierarchy, and war; as well as reverence for particular sacred texts, such as the Torah and Talmud in the case of the former, or the Bible and the National Enquirer in the case of the latter.
Addendum: As Deborah909 suggests, the use of this term (especially by Christians) is somewhat questionable; while Christianity historically emerged out of Judaism the modern forms of the two do not have all that much in common. (See There is no "Judeo Christian" ethic for a more detailed discussion of the problem.)
It is my impression that when Christians -- and politically conservative Jews (such as Joe Lieberman) (not to be confused with Conservative Jews) -- make reference to "Judeo-Christian" ethics or culture, they are referring largely to the legalistic provisions of the Torah combined with their moralistic interpretations by Christian churches. | 
