Unleavened bread is bread made without anything that makes it rise — no yeast, no baking powder. So it stays flat and thin, and it is usually firm or chewy rather than soft and airy. Think of the flat breads people eat all over the world: Indian roti and papadum, Mexican corn tortillas, Jewish matzo, the wrappers for 蔥油餅 before the frying. The word is almost only ever used with the word 'bread' after it — 'unleavened bread' is a set phrase. You will meet it most in two places. One is religion and history: unleavened bread matters a great deal in Judaism, because the story is that people leaving Egypt had no time to wait for dough to rise, and it is still eaten at Passover; it also appears in Christian communion in some churches. The other is cooking writing, where a food writer might say a bread is unleavened to explain why it is flat. In ordinary conversation people almost never say it — they just say 'flatbread', or name the bread. It is a slightly formal, slightly bookish word, and reading it in the Bible is how most English speakers first meet it. The plain word inside it is 'leaven', which means the yeast or starter that makes dough rise; 'leaven' also has a nice figurative use — to leaven something is to lighten it, as in 'his speech was leavened with jokes' — but 'unleavened' is not usually used figuratively that way.

無酵的、不發酵的（如無酵餅）；台灣講餅本身時多半直接說「未發酵的麵餅」或「無酵餅」，後者是聖經譯本的固定用詞