After the avelut [mourning] period is complete, the family of the deceased is not permitted to continue formal mourning; however, there are a few continuing acknowledgments of the decedent. Every year, on the anniversary of the death, family members observe the deceased’s Yahrzeit (Yiddish, lit. “anniversary”). On the Yahrzeit, sons recite Kaddish and take an aliyah (bless the Torah reading) in synagogue if possible, and all mourners light a candle in honor of the decedent that burns for 24 hours. In addition, during services on Yom Kippur, Shemini Atzeret, the last day of Passover, and Shavu’ot, after the haftarah reading in synagogue, close relatives recite the mourner’s prayer, Yizkor (“May He remember…”) in synagogue. Yahrzeit candles are also lit on those days.
Kaddish
Kaddish is commonly known as a mourner’s prayer, but in fact, variations on the Kaddish prayer are routinely recited at many other times, and the prayer itself has nothing to do with death or mourning. The prayer begins “May His great Name grow exalted and sanctified in the world that He created as He willed. May He give reign to His kingship in your lifetimes and in your days …” and continues in much that vein. The real mourner’s prayer is E-l Maleh Rachamim, which is recited at grave sites and during funerals.
Why, then, is Kaddish recited by mourners?
After a great loss like the death of a parent, you might expect a person to lose faith in G-d, or to cry out against G-d’s injustice. Instead, Judaism requires a mourner to stand up every day, publicly (i.e., in front of a minyan, a quorum of 10 adult men), and reaffirm faith in G-d despite this loss. To do so inures to the merit of the deceased in the eyes of G-d, because the deceased must have been a very good parent to raise a child who could express such faith in the face of personal loss.
Then why is Kaddish recited for only 11 months, when the mourning period is 12 months? According to Jewish tradition, the soul must spend some time purifying itself before it can enter the World to Come. The maximum time required for purification is 12 months, for the most evil person. To recite Kaddish for 12 months would imply that the parent was the type who needed 12 months of purification! To avoid this implication, the Sages decreed that a son should recite Kaddish for only eleven months.