[shàng xià]
（职务、辈分上的高低） high and low; old and young
the whole nation
举国上下
All members of the family, old and young, are very pleased.
全家上上下下都很高兴。
（从上到下） from top to bottom; up and down
The water tower is fifty metres high.
这个水塔上下有50米。
（从高到低或从低到高） go up and down
With an elevator in the skyscraper, we can easily go up and down.
摩天楼里有电梯，上下很方便。
（程度高低） relative superiority or inferiority
equally matched; about the same
不相上下
hard to tell which is better
难分上下
（用在数量词后面） about; or so; or thereabouts
about thirty years old; thirty or so
30岁上下