Yizkor literally means “will rememeber”. It is also a name of a prayer said on behalf of departed relatives. The Yizkor prayer is recited during synagogue services on Yom Kippur, Shemini Atzeret, the eighth day of Passover, and the second day of Shavuot. One may say Yizkor privately at home. The evening before Yizkor it is customary to light a memorial candle – Ner Neshamah – נר נשמה
It has been customary for all congregants other than those who would be saying Yizkor, to leave the synagogue while it is said. Lately though, there have been calls to retract this custom so all congregants will stay during the Yizkor.