A Slava is the celebration of the family's patron saint. It's primarily known as a Serbian custom: when the disciples of Sts. Cyril and Methodius were converting ancient Serbia, they replaced the pagan custom of the household divinity with a family patron saint. However, this is not an exclusively Serbian custom, as it is also known among the Bulgars, the Albanian, and even in parts of Greece and Romania. A saint was determined by the day on which the household was baptized. Serbs do not celebrate a family Slava instead of an individual nameday (onomastik), but rather in addition to their namedays. The most common Slavas are St. John the Baptist, St. George, and St. Nicholas.
The Serbs in particular, but also many Albanians, Bulgars, and even Romanians and Greeks, observe not only their individual nameday (onomastik), but also their family patronal feast, which is dedicated to saint of feast commemorated on the day in which their first ancestor was baptized. Families keep with great honor an icon of this saint or feast which is passed from generation to generation, and observe the day with a Krsna Slava Service at home, which is lead by the priest, or in his absence, by the domachin (head of the family).