The Serbian tradition of burning an oak log on Christmas Eve is called badnjak.
A badnjak is traditionally an oak log or branch ceremonially cut, brought home, and placed on the fire on Christmas Eve. The burning is accompanied by prayers and wishes for health, happiness, prosperity, abundant crops, and a thriving household. The practice is central to Serbian Christmas celebrations and has regional variations.
Traditionally, the head of the household selected and felled a young, straight oak tree on Christmas Eve morning. Turkey oak is especially common, although other oak species—and, in some regions, other trees—may be used. The log could burn through Christmas Day, with sparks symbolically linked to future prosperity.
Modern homes often cannot accommodate a large hearth log, so the badnjak may be represented by a bundle of oak twigs with brown leaves. Public Serbian Orthodox celebrations also burn badnjaks in churchyards. The term is sometimes compared with a Yule log, but the Serbian ritual has its own Orthodox and South Slavic traditions.