On a graph, the y-axis is the line that runs up and down the side, with numbers marked along it. Its partner is the x-axis, the line that runs left to right along the bottom.

On a graph 在圖表上，the y-axis is the line that runs up and down the side y-axis是沿著側邊上下延伸的那條線，with numbers marked along it 上面標著數字。Its partner is the x-axis 它的搭檔是x-axis，the line that runs left to right along the bottom 是沿著底部左右延伸的那條線。

Together they let you fix any point on the graph: how far across (x) and how far up (y). Usually the y-axis carries the thing you measured — sales, temperature, height — while the x-axis carries what you measured it against, most often time. So in "sales rose sharply", the rise you see is movement up the y-axis.

Together they let you fix any point on the graph 兩條線合起來就能定出圖上任何一點：how far across (x) and how far up (y) 橫向多遠（x）、縱向多高（y）。Usually the y-axis carries the thing you measured 通常y-axis放的是你測量的東西——sales, temperature, height 像銷售額、溫度、身高——while the x-axis carries what you measured it against 而x-axis放的是你拿來對照的東西，most often time 最常見的就是時間。So in "sales rose sharply" 所以在「sales rose sharply」（銷售額急升）這句話裡，the rise you see is movement up the y-axis 你看到的上升就是在y-axis上往上移動。

It is a countable noun, and it almost always takes the: the y-axis, plural the y-axes (say "AX-eez"). Common phrases: on the y-axis, along the y-axis, label the y-axis, the y-axis shows temperature in degrees.

It is a countable noun 它是可數名詞，and it almost always takes the 而且幾乎都會加the：the y-axis, plural the y-axes (say "AX-eez") the y-axis，複數是the y-axes（唸成「AX-eez」）。Common phrases 常見的用法：on the y-axis, along the y-axis, label the y-axis, the y-axis shows temperature in degrees on the y-axis、along the y-axis、label the y-axis、the y-axis shows temperature in degrees這些。

Written with a small y and a hyphen; you may also see the y axis with no hyphen, and in books the letter is often italic.

Written with a small y and a hyphen 寫的時候用小寫y加連字號；you may also see the y axis with no hyphen 你也可能看到沒有連字號的y axis，and in books the letter is often italic 書裡這個字母常常是斜體。

In maths, the y-axis is also the vertical line through the middle of a coordinate grid — the line where x = 0 — with positive numbers above zero and negative numbers below.

In maths 在數學裡，the y-axis is also the vertical line through the middle of a coordinate grid y-axis也是坐標格正中間那條垂直線——the line where x = 0 也就是x = 0的那條線——with positive numbers above zero and negative numbers below 零以上是正數，零以下是負數。