What does this graph mean? I know little about economics and am very confused on what this graph represents. 
 I found it when I saw that the President had tweeted it and was wondering what it mean.  Specifics what "Jobs plentiful" and "jobs hard to get" are measured in.
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.