What does this graph mean?
The data plotted in the graph are based on a consumer survey conducted by Conference Board. They ask consumers how hard it to get a job. If 34.1% of people say that "jobs are plentiful" and 18% of people say "jobs are hard to get" then the figure would plot a value of $34.1-18=16.1$.

The figure originally comes from this Bloomberg article, but you can read a little more about the underlying data here.