about $2.25 at the Jewish bakery
Jewish
They don't symbolize anything, some people just like poppy or sesame seeds.
15th Century, Eastern Europe. There is also another tradition. The word challah is found in Bible. Leviticus 24:5-7.
Because it was invented by Jews for use at festive meals. The name comes from the small piece of dough that is removed before the bread is baked, as commanded in Numbers 15:17-21.