Flat means horizontal and not upright.
水平的 • Two men near him threw themselves flat. 他旁边的两个人一下子平趴在了地上。
If someone sings flat or if a musical instrument is flat, their singing or the instrument is slightly lower in pitch than it should be.
(演唱或乐器) 比标准音低地 He flatly refused to discuss it. 他断然拒绝讨论此事。
You can refer to one of the broad flat surfaces of an object as the flat of that object.
平面 His mother looked ten years younger in jeans and flats. 他的母亲穿着牛仔裤和平底鞋,看上去年轻了10岁。
A flat is a set of rooms for living in, usually on one floor and part of a larger building. A flat usually includes a kitchen and bathroom.
公寓套房 That allegation is a flat-out lie. 那一个指控是彻底的谎言。