The R'uustai is the Klingon rite of bonding, or "The Bonding" where two Klingons join together to become brothers, one entering the other's house. Candles are lit and then words spoken to honor the memory of the participants' mothers -- they become one in house.
In 2366, Lieutenant Worf and Jeremy Aster performed this rite after Jeremy's mother was lost while on an away mission.(TNG: "The Bonding")