y is the "ordinate".
See also:
This article (or an earlier version of it) contains material from FOLDOC, used with permission. Modify if needed.
... 24, 32.3% from 25 to 44, 21.1% from 45 to 64, and 11.8% who are 65 years of age or older. The median age is 37 years. For every 100 females there are 95.2 males. Fo ...