Challah is a special bread in Jewish cuisine, usually braided and typically eaten on ceremonial occasions such as Sabbath and major Jewish holidays (other than Passover). Ritually-acceptable challah is made of dough from which a small portion has been set aside as an offering. Similar braided breads - such as kalach, kalács, kolach, or colac - are found in Eastern Europe, though it is not clear whether these influenced or were influenced by the traditional Ashkenazic challah. (source)