A Bark Mitzvah is a pseudo-traditional observance and celebration of a dog's coming of age, as in the Jewish traditional Bar Mitzvah and Bat Mitzvah. The term has been in use since at least as early as 1997, and Bark Mitzvahs are sometimes held as an adjunct to the festival of Purim.
The Bark Mitzvah is a celebration not necessarily held in conjunction with a specific age but can occur when the dog turns 13 months or 13 years of age. This is equivalent to about 91 dog years. During some Bark Mitzvahs, dogs wear a tallit, a ritual prayer shawl worn during Jewish religious services and ceremonies. A male dog wears a specific yarmulke, a thin skullcap.
Read more at http://en.wikipedia.org/wiki/Bark_Mitzvah