The 10th day of the Jewish month of Shevat (Yud Shevat in Hebrew) is a most significant date on the chassidic calendar. It is the anniversary of passing (yahrtzeit) of the sixth Lubavitcher Rebbe, Rabbi Yosef Yitzchak Schneersohn (1880-1950), of righteous memory.
It is also the day when, in 1951, the seventh Rebbe, Rabbi Menachem Mendel Schneerson (1902-1994), of righteous memory, formally accepted the leadership of Chabad-Lubavitch with a historic discourse (maamar) and address at a gathering marking the first anniversary of his predecessor's passing.