Y axis is Height (or whatever you've set in the "Show by drop down" and X axis is the title of the graph, "Share of possible matches removed via filters, %". Hover over a point and the graph becomes much easier to understand.

E.g. one point shows

> Hispanic men, 25-29 years old, 6'0"-6'1". Filtered out by 9% of possible matches

Each of the circles represents a group that is defined by a permutation of Race/Gender/Age/Height. I think size of circle represents size of that population in the dataset. In the case of my example, the circle for "Hispanic men, 25-20 years old, 6ft-6ft1in" was small, so there probably aren't many men fitting that specific combination in the data set. You also see intuitively that the circles for men 5'5" or shorter are small and the circles for women 6'0" or taller are smaller, corresponding to our intuitions that men that short or women that tall are less common in the overall population.