A biscuit is a small flat cake that is crisp and usually sweet.
N-COUNT
烤饼；小圆面包
A biscuit is a small round dry cake that is made with baking powder, baking soda, or yeast.
PHRASE
（强调吃惊）竟然做出这种（愚蠢、粗野或自私的）事情
If someone has done something very stupid, rude, or selfish, you can say that they take the biscuit or that what they have done takes the biscuit, to emphasize your surprise at their behaviour.